I can say the same thing, with different intonation, and mean something entirely different - "How do you know?" "How do YOU know?" "How do you KNOW?" - but the one in which I'm most interested, is, "HOW do you know?"
The Judeo/Christian/Islamic god is said to be omniscient, which means he knows everything - how does anyone know this? How does this god know what he knows? How, as Darkmatter 2525 said, does he know that there isn't something that he doesn't know that he doesn't know? You know?
I found this fascinating, and hope that anyone who watches it will come away with just a little more knowledge about the Human animal, or as Tim Minchin put it, "the monkey with shoes":