Oh man. We're living the Zasalamel lifestyle, are we? Yeah, I'd see everything. Everything! And then, I'd start my own religion. With me as a demigod! (not a full-time god, just in case the Big Guy is real and smites my immortal ass for it, and also people will ask me for stupid stuff less).
I'd then begin absorbing all knowledge in the world, haphazardly until I've gotten it all. In the meantime, I'd have tower of Babel/ICO/Shadow of the Colossus/Final Fantasy/etc.-style gigantic buldings built in my name, like a hundred thousand skyscrapers on top of each other but carved out of pure stone. I'd let vegetation grow upon it in specifically built gardens so Earth's gigantic willy (as the rabble will call it) will last as long as I do, or care to stay on Earth. I'd just build and build and build... no, wait, terrorists would try to destroy my beautiful creations, so the only way to stop them would be to kill every living human being on Earth.
Thus would the self-proclaimed demi-god with all knowable knowledge stuffed in his skull go mad and become worse than a hundred Hitlers, with the added benefit of not having hilarious facial hair, so no-one would be laughing as they were exterminated.