tec/Tam...
The question isn't about God knowing about his own existence.
Any conscious "person" at least knows they exist.
What is not known, or is even knowable by ANY conscious "person", is the nature of his/her/its own existence.
For example, the old quote attributed to the chinese philosopher Zhuangzi...
"Once upon a time, I, Chuang Chou, dreamt I was a butterfly, fluttering hither and thither, to all intents and purposes a butterfly. I was conscious only of my happiness as a butterfly, unaware that I was Chou. Soon I awaked, and there I was, veritably myself again. Now I do not know whether I was then a man dreaming I was a butterfly, or whether I am now a butterfly, dreaming I am a man. Between a man and a butterfly there is necessarily a distinction. The transition is called the transformation of material things."
http://en.wikiquote.org/wiki/Zhuangzi
This illustrates the problem that the movie The Matrix wrestles with.
This is why any self-proclaimed God can NEVER know whether or not there may be still OTHER Gods higher than him or herself.
So when Isaiah ostensibly quotes Jehovah at Isaiah 44:6-7:
“This is what Jehovah has said, the King of Israel and the Repurchaser of him, Jehovah of armies, ‘I am the first and I am the last, and besides me there is no God. And who is there like me? Let him call out, that he may tell it and present it to me..."
Jehovah is just making an assertion to the ones in his own Matrix. He can never know unless someone were to "... call out, that he may tell it and present it to [him]. "
So one can speak of Jehovah's omniscience as "knowing all things which are knowable", but the knowledge of "knowing" whether one is or is not living in a Matrix-like situation is something which is simply not "knowable". This is why Jehovah can never really know that he is the "first and the last".
So Jehovah's doing a Taxi-Driver to humanity.