How Can God be sure that He is God?

No being can step outside of their sensory and experiential limits and it doesn't help that God might 'feel' like He has no such limits, that's not something He can demonstrate to Himself. God might just be a construct made to believe that He is God and if the construction is good enough He can never know otherwise.

Muhammad never lied.

I suppose it depends on your definition of God. A traditional Christian God, for example, would be omniscient, so He would know everything including the fact that he was God. I'm not a believer mind you, so I don't really believe in a God at all, but I think it depends largely on what you consider a God to actually be, and then by extension you could draw some conclusions about His character

How would God actually know He was omniscient? Bear with me here. How would He know, for example, that He hadn't been created by some more powerful entity which was capable of so constructing His faculties so as to make Him believe He was omniscient and thus 'knew' He was omniscient (even though He wasn't)? I think this is a genuine epistemological issue for God should He exist.

Accepting the premise that God is an entity that exists, the very definition of omniscience is that he would be all knowing. This would include a knowledge of the entity that created him. The thing I would argue with this is, if 'God' was created by a more powerful entity, then the God that is accepted by traditional beleif would not be God at all, and that title would then fall to the more powerful entity that constructed him, and with that in mind you would face an endless loop of cyclic questioning about whether or not that entity was created by a more powerful one. I think the whole concept behind the traditionalist God is that He, if he exists, requires no justification. We are considering God in terms of a comparatively narrow Human perspective, when in reality if God were a real deity then he would be outside the laws of our understanding and applying Human logical reasoning would become irrelevant. His mind would be infinfintely more complex than our own and, being on an entirely seperate plane of existence, it would stand to reason his logical process would be different from our own also

Not sure if you're agreeing with my hypothesis - that it's not possible for an entity to 'know' that it has unbounded faculties even when it might believe it does, hence causing it to always fall short of omniscience.

The trap is sprung when transplanting human attributes into God, including logic and psychology.

The entire premise is flawed because it assumes a human can know more and be more aware than God.

Omnipotence is by definition not bounded by universal laws governing humans.

But I've done none of that. I've identified 'faculties', does God not have any faculties?

Faculties are a human definition attributed to God by a human.

God is omnipotent and can therefore have both infinite faculties simultaneously with none at all.

Ok, but on that basis anything claimed about God is defined by us humans, including, for example, your claim that God is 'omnipotent'. Following your logic nothing can be said about God because we can't actually know anything about Him. It's therefore possible that God is actually a construct of some other entity unknown to us and, possibly, unknown to the thing we call 'God'.