how can a being that has always existed know anything about its own knowledge? how does god know that he actually knows everything? how does god know that his understanding and judgments on any and all possible things is actually correct??
Alpha God created all that exists (besides itself, but void needn't to be created). Considering this, it grants knowledge of it. If you build something you can know pretty much everything about it that came from your hands (if you insist that it's not true because you wont know every little detail of it, but emphasize on knowing most or all of the portion you created. God made existence, it has full awareness of it all because the entirety of the universe was created by it.
how does god know that he does not actually have a creator that created him to believe he always existed and is all knowing simply as a practical joke?
Concept of my God of nothing (void) aside, I would say that it's obvious that God existed in nonexistence before creating existence. Without reality being built, there can be no cause of the cause. The cause (God) happened simultaneously as the effect (the universe). Nothing could have created God because God was the first thing existing.
why do you expect god thinks at all?
Most people believe God is a conscious being, mainly because if God was just an active, unaware force then it would make existence a mistake, a flaw in the void, an accident. It may also extend that the definition of God would hardly fit, but that word is thrown around too much these days.
Because God is conscious, thinking is included, all conscious beings have thoughts, they are a major part of consciousness.
why do you expect god knows everything?
As said, God knows everything because existence was created by it, and therefore God knows all about it.
why do you expect god even exists?
Just seems logical to me, but it's obviously not for everybody.
what does god base his knowledge on other than himself? nothing. there is no proof his knowledge is actually correct, because god doesn't know any better than what he knows.
That is like saying a fiction author might be wrong about the protagonist's life or thoughts.