Someone claimed their Hindu guru is omniscient.

Soh replied:

as for claims of omniscience -- the jains, etc claimed so, but were ridiculed in the suttas. 

https://suttacentral.net/mn76/en/sujato?lang=en&layout=plain&reference=none&notes=asterisk&highlight=false&script=latin

“Sandaka, take a certain teacher who claims to be all-knowing and all-seeing, to know and see everything without exception, thus: ‘Knowledge and vision are constantly and continually present to me, while walking, standing, sleeping, and waking.’ They enter an empty house; they gets no almsfood; a dog bites them; they encounters a wild elephant, a wild horse, and a wild cow; they ask the name and clan of a woman or man; they ask the name and path to a village or town. When asked, ‘Why is this?’ they answer: ‘I had to enter an empty house, that’s why I entered it. I had to get no almsfood, that’s why I got none. I had to get bitten by a dog, that’s why I was bitten. I had to encounter a wild elephant, a wild horse, and a wild cow, that’s why I encountered them. I had to ask the name and clan of a woman or man, that’s why I asked. I had to ask the name and path to a village or town, that’s why I asked.’ Not only did the Buddha deny this kind of strong omniscience, he took pains to point out its absurdity.

A sensible person reflects on this matter in this way: ‘This teacher makes such a claim, but they answer in such a way. This spiritual life is unreliable.’ Realizing this, they leave disappointed.

…

the buddhist explanation is much more sensible:

….

Krodha/Kyle Dixon wrote in 2023: 

In buddhadharma, omniscience (sarvajñāna) means a knowledge of the nature of phenomena, and a knowledge of all the paths and stages to buddhahood. Omniscience does not mean that the Buddha knows the number of worms in the ground, as Dharmakīrti apparently quipped.

Further, Ācārya Malcolm says regarding omniscience in Buddhism:

The definition of Buddha's omniscience does not come from sūtra, it comes from śastra. And it has limits. Strictly speaking it is knowledge of all phenomena. But "all phenomena" simply refers to one aggregate, one sense base, and one sense element. It does not refer to everything in the universe, known and unknown. It refers to that which is one's personal range. Thus, to bring up another contentious point, the Buddha can be "incorrect" (that is to say, bow to conventions of his day) about Meru, but still be entirely correct about the paths and stages. We do not need to ascribe super powers to the Buddha even he didn't claim.

——

That person said:

Well all the monks of this guru experienced that in first person

There was a ceremony in which all of his monks were put in lines and he started talking all stuff from them that they did since they were a child

And when going in new places he was a waterfall of knowledge about nature ang geology of every place they visited even if nobody has been there before

Soh: 

I would be doubtful but even that is true, it is not omniscience. Omniscience would mean he would know what kind of technologies will be invented in 100 years, what are all the world events that will occur in the next year, so on and so forth. If such beings exist why wouldn’t they have revealed these knowledge to us? Why back in olden days, didn’t these people reveal to us the structure of the universe, that planet earth is one among several that is round and revolves around the sun, instead of being a flat earth universe where sun and moon revolves around us?

And to me all these are just mundane siddhis, nothing to do with awakening and liberation.

Susima sutta discusses well https://www.dhammatalks.org/suttas/SN/SN12_70.html

If such omniscient beings exist, they will never need to ask anyone a question anymore, they will never make a single mistake or forget something, they will never get lost in the forest or need to rely on gps when traveling, they will not need to accept donations as they can know where hidden diamonds and gemstones are found in the earth, or they can buy a winning lottery ticket to a million bucks, and so on and so forth.

Even the buddha and ananda ridiculed such notions

Such beings also do not have to see doctors or go to the hospital for diagnosis, they will know the cure to their illness, etc, as they simply know everything. Even illnesses that has never been diagnosed in history would be known and uninvented medicines will be known. Then why don’t they share these medicines as well

Etc

So for me it is quite ridiculous a notion to entertain

Lots of claimants in the spiritual market and even a title like arahantship and stream entry is so much misunderstood these days

I don’t blindly believe in claims but investigate and question and find out

——

Update:

https://suttacentral.net/mn71/en/sujato?lang=en&layout=plain&reference=none&notes=asterisk&highlight=false&script=latin

Middle Discourses 71

To Vacchagotta on the Three Knowledges So I have heard. At one time the Buddha was staying near Vesālī, at the Great Wood, in the hall with the peaked roof.

Now at that time the wanderer Vacchagotta was residing in the Single Lotus Monastery of the wanderers. Then the Buddha robed up in the morning and, taking his bowl and robe, entered Vesālī for alms. Then it occurred to him, “It’s too early to wander for alms in Vesālī. Why don’t I visit the wanderer Vacchagotta at the Single Lotus Monastery?” So that’s what he did.

Vacchagotta saw the Buddha coming off in the distance, and said to him, “Let the Blessed One come, sir! Welcome to the Blessed One, sir! It’s been a long time since you took the opportunity to come here. Please, sir, sit down, this seat is ready.”

The Buddha sat on the seat spread out, while Vacchagotta took a low seat and sat to one side. Then Vacchagotta said to the Buddha:

“Sir, I have heard this: ‘The ascetic Gotama claims to be all-knowing and all-seeing, to know and see everything without exception, thus: “Knowledge and vision are constantly and continually present to me, while walking, standing, sleeping, and waking.”’ I trust that those who say this repeat what the Buddha has said, and do not misrepresent him with an untruth? Is their explanation in line with the teaching? Are there any legitimate grounds for rebuke and criticism?”

“Vaccha, those who say this do not repeat what I have said. They misrepresent me with what is false and untrue.”

“So how should we answer so as to repeat what the Buddha has said, and not misrepresent him with an untruth? How should we explain in line with his teaching, with no legitimate grounds for rebuke and criticism?” “‘The ascetic Gotama has the three knowledges.’ Answering like this you would repeat what I have said, and not misrepresent me with an untruth. You would explain in line with my teaching, and there would be no legitimate grounds for rebuke and criticism.

For, Vaccha, whenever I want, I recollect my many kinds of past lives. That is: one, two, three, four, five, ten, twenty, thirty, forty, fifty, a hundred, a thousand, a hundred thousand rebirths; many eons of the world contracting, many eons of the world expanding, many eons of the world contracting and expanding. I remember: ‘There, I was named this, my clan was that, I looked like this, and that was my food. This was how I felt pleasure and pain, and that was how my life ended. When I passed away from that place I was reborn somewhere else. There, too, I was named this, my clan was that, I looked like this, and that was my food. This was how I felt pleasure and pain, and that was how my life ended. When I passed away from that place I was reborn here.’ And so I recollect my many kinds of past lives, with features and details.

And whenever I want, with clairvoyance that is purified and superhuman, I see sentient beings passing away and being reborn—inferior and superior, beautiful and ugly, in a good place or a bad place. I understand how sentient beings are reborn according to their deeds. And I have realized the undefiled freedom of heart and freedom by wisdom in this very life. I live having realized it with my own insight due to the ending of defilements. ‘The ascetic Gotama has the three knowledges.’

Answering like this you would repeat what I have said, and not misrepresent me with an untruth. You would explain in line with my teaching, and there would be no legitimate grounds for rebuke and criticism.”

When he said this, the wanderer Vacchagotta said to the Buddha, “Master Gotama, are there any laypeople who, without giving up the fetter of lay life, make an end of suffering when the body breaks up?”

“No, Vaccha.”

“But are there any laypeople who, without giving up the fetter of lay life, go to heaven when the body breaks up?”

“There’s not just one hundred laypeople, Vaccha, or two or three or four or five hundred, but many more than that who, without giving up the fetter of lay life, go to heaven when the body breaks up.”

“Master Gotama, are there any Ājīvaka ascetics who make an end of suffering when the body breaks up?”

“No, Vaccha.”

“But are there any Ājīvaka ascetics who go to heaven when the body breaks up?”

“Vaccha, when I recollect the past ninety-one eons, I can’t find any Ājīvaka ascetics who have gone to heaven, except one; and he taught the efficacy of deeds and action.”

“In that case, Master Gotama, that sectarian fold is empty even of the chance to go to heaven.”

“Yes, Vaccha, that sectarian fold is empty even of the chance to go to heaven.”

That is what the Buddha said. Satisfied, the wanderer Vacchagotta was happy with what the Buddha said.