Does God know what it feels like to not know everything? If not than he doesn't know everything. But
if he does know what it feels like to not know everything, then he doesn't know everything.
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Being an atheist, a fortiori I do not believe that any god knows anything.
However, taking your argument on its own merits,
(1) I agree that if god doesn't know what it feels like not to know everything, then he doesn't know
everything.
(2) I don't agree that if god does know what it feels like not to know everything then he doesn't know
everything. I know my next door neighbour has brown hair. I can remember what it was like not
knowing her, before I met her. So I know what it is like not to know she has brown hair; but that
doesn't prevent my knowing that she does. So there is no principled reason why a god cannot both
know everything and know what it is like not to know everything.