[Serious] Could an omnipotent and omniscient god prove that he was God?

[Neo-Scholastic]

I'm still having a hard time understanding how "existence exists" explains why/how particular things exist. Yes, existence is real, but so what? How is this more explanatory than saying God exists (for example)?

For example, how do you get from "existence exists" to "this local universe exists". How does a principle do that exactly?

It doesn't.  That's not it's job.  It's job as I said is to identify a general truth on which other truths rest.  How you get to further knowledge is by the same process of looking at reality and identifying what you perceive.  We don't just recognize that existence exists and deduce everything else from that recognition.  That's not the way knowledge works.  We learn almost everything inductively.  Only after we've done induction can we apply that inductive knowledge to particulars.  We can't say existence exists and then jump straight to why/ how does the local universe exist.  What is a universe, what does local mean?  What is causation?  Before we get to those concepts we've already made a long chain of discoveries that lead up to those questions and when we get to them we answer them, if they are not improper questions, by looking to reality.  We don't start with nothing and then seek a reason for why existence exists.  You have to start with existence and then see what else you can learn about it.  The question of what came before everything and what caused it is an improper question because it makes use of stolen concepts.  To steal concepts is to make use of them while ignoring their roots including the recognition that existence exists.

You mean like poposing a being whose essense and existence are the same?....sounds very familiar. Could be a stolen concept, yes?