If you were arguing along the lines of "God is not not all-knowing", you would have a point that its negation would carry the meaning that "God is all-knowing". But what you're trying to smuggle in is more along the lines of "God is not not all-unknowing", which is not the same thing at all.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
