By perfect knowledge I mean you know it by heart, and have absorbed all the meaning in it. No encyclopedias!

I'd probably say the Bible. I'm agnostic, but the sheer amount of literature, art, and philosophy inspired by it makes it an obvious choice in my mind. But maybe that's cheating, since it's technically +60 smaller books.

I could also go with something like Thinking Fast and Slow by Daniel Kahnemann, that would be great too. Or Ovid's Metamorphosis. Or Fifty Shades of Grey, just to be edgy. Dunno, what about you?