Well, lyrics sites are notorious for getting lyrics wrong. It sounds like he says "want it" to me, but even ignoring that, I'm really not sure how you can tell the difference between "wanna" and "wannit".
I've found this site to be the most accurate and revealing. In it he explicitly says "want it for you". But it also says he got intentionally ambiguous with the title just to be controversial. http://www.songfacts.com/detail.php?id=45900