A being can only knows what it knows, correct? And a being does not know what it does not know, correct? A being’s scope of knowledge is limited to what it knows. A being cannot know what lies outside of that scope. Imagine this: Of everything which can be known, there are two categories: Category A, which consists of things a being knows; and category B, which consists of things a being does not know. This makes sense, yes?

There is at least one thing that no being knows. No being can know if there is something it doesn’t know. Remember what I said about Category A and Category B. Now, let’s apply that to a being that thinks it knows everything. For everything in Category B, an omniscient being doesn’t know it. You might say, “There’s nothing in Category B!” Perhaps, but listen to this. Even a supposedly 'omniscient' being cannot know if there’s something in category B. Whether or not something truly exists in Category B is irrelevant.I’m just saying a being cannot know if there’s something in Category B – that would mean a being knows what it doesn’t know.

You cannot use what you know to decide what you do not know. That’s the case for every being. You cannot use your knowledge your justify that your knowledge is infinite. So, It's impossible to even know if Category B even exists. Therefore, a being, even a supposedly omniscient being,  can not know if there’s something it does not know. That means that there IS something that the being does not know. A being cannot know for sure if it is truly omniscient. Thus, it’s impossible for a being to be omniscient in the first place.

I’m not saying a being doesn’t know what it doesn’t know. The word ‘what’ would require there to be something that a being doesn’t know. I’m not saying that. I’m saying a being doesn’t know if there’s something it doesn’t know. The word ‘if’ refers to the possibility of there being something it doesn’t know. And no being can know what may lie outside of His knowledge.

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Too Long; Didn't read

How can a being know if it doesn't know something? 

A being's beliefs are only based on His knowledge. But How does he know if His knowledge truly includes everything there is to be known? You cannot use your knowledge to prove that your knowledge is infinite

An omniscient being can not know what the universe would be like without its influence.

I think this quote is fitting

" All intelligent sentient beings must realize that without verification from other beings than itself or from science, it cannot know if it is correct in its world view. It doesn't matter how intelligent or knowledgeable a being is - if that being wants to verify its knowledge to make sure that it is correct then it needs to look to something more intelligent than itself, or to science. But what if you are the creator of science? You couldn't then use your own construct to test if your own construct was true, it would be an invalid test. If god attempted to find out if it did indeed know everything, it would realize that it has no way to know. How does it know it knows everything? It merely thinks it does. God has no test, method or possibility of finding out if it does indeed know everything. It could itself be a created being, with another creator hiding secretly behind it. It wouldn't know. In short, it does not and cannot know if this is true. God does not know everything and is not omniscient. In fact, no being can know everything because no being, however creative or perfect, can verify that its own knowledge is complete"

http://www.vexen.co.uk/religion/omniscience.html

"A being can only knows what it knows, correct? And a being does not know what it does not know, correct? So far, everything is fine. A being’s scope of knowledge is limited to what it knows. A being cannot know what lies outside of that scope. Of everything which can be known, there are two categories: Category A, which consists of things a being knows; and category B, which consists of things a being does not know. This makes sense, yes?
You may be thinking: In relation to an omniscient being, category B does not exist. There is nothing which it does not know. That’s not the point right now. The point is: A being cannot know what it does not know. A being cannot know what’s in Category B or if anything is in Category B at all. This applies to all beings. You may say it doesn’t apply to an omniscient being, but keep reading."

The argument falls when you you make the argument that assumes he doesn't know x at all. This goes against the very definition omniscient. There is no argument to assume he doesn't know anything and seems to be very circular coming from your mind and not actual reality of the definition.

If I knew everything it would be incoherent to say that I don't know something.

It's like saying is possible to eat 5 if you can't eat 5 then you can't eat everything.

But it cannot know if it doesn't know. No being can know if there exists things which it doesn't know.

How could someome truly know he/she knows everything? It's not possible! It's not possible to say there's nothing which exists outside of your scope of knowledge. Becuase you have no knowledge of what lies there

"But it cannot know if it doesn't know"

How do you know "it" doesn't know? And if explained why would some that was knew everything not know it just seems like a claim. I are we assuming he can't know something based on the human limited mind or something omniscient because by defintion he would know it even if you think he couldn't be he would.

"But it cannot know if it doesn't know"

How doesn't he know? What doesn't it know your just saying he doesn't know x without any reasoning it just seems to be claiming without telling us why. Just saying he doesn't know x doesn't mean he doesn't know x just means you think he doesn't without an actual argument.Seems like the argument falls on you to tells us what this unknown is  without exposing our non-omniscient mind.

Again the defintion tells us he knows everything and you tells us nothing he can't know. You just say he can't know this "unknown" without explaining this unknown besides something made in the mind and not in reality. This unknown your speaking of doesn't exist outside of your mind if we don't know this unknown based on human mind. This whole argument is based on limited mind vs omniscient and by very defintion something you think would be unknown wouldn't be for omniscient. You would have to downplay omniscients for this to work like he can only know what is humanly possible. But it's not so the argument falls apart. There is no reason to think omniscient is false if you take away it's properties. It's a straw man basically.

It doesn't matter if there really is something He doesn't know. The point is He doesn't know if there is something He doesn't know. He may think he knows everything. But He has no way of knowing He knows everything. No being can know what lays beyond His realm of knowledge. I'm not sayying there is something beyond His realm of knowledge. I'm saying He doesn't know if there is something beyond His realm of knowledge. He cannot prove to Himself that there is nothing He doesn't know.

For all He knows, there are dozens of facts He doesn't know. He just doesn't know he doesn't know because...He doesn't know about them. Do all he facts really exists. No being can know. That's the point.

A being may think he's omniscient. But that's only based on His own knowledge - and a being cannot know if His knowledge covers everything that exists. And no, you cannot say He knows everything because He knows everything. That claim is based on the presumption that the being really does know everything, which is impossible to prove.

Again, I'm not asserting that there IS something that exists ouside of an omniscients's mind. I'm asserting that an omniscient cannot know IF there is something which exists outside of His mind. It cannot know if there are things it does not know. And it's illogical for a being to use His knowledge to determine if He knows everything, because He doesn't know if His knowledge is infinite to begin with.

P.S. You don't have to re-quote my entire post. That's the point of quoting in the first place.

This argument, to anyone who it matters to, would simply reply with "He is greater than you. Humans cannot understand what his Will is."

If a being is truly omniscient then it knows that it knows everything. Since this knowledge is part of "everything", an omniscient being by definition knows this. You know?