In 'Pulp Fiction', the movie doesn't really give a detailed account of the exact book Vincent is reading. It could be some kind of pulp novel, given the name of the movie, but without more information, it's hard to say for sure. Maybe it was just a prop to add to the overall seedy and mysterious atmosphere of the character.
Yes, he might be. In 'Pulp Fiction', Vincent Vega is a key character, and if the book is related to the story of 'Pulp Fiction', it's very possible that there's a scene or description of him reading it.
I have no definite answer. It could have been a random pulp fiction book chosen to add an element of mystery. We just don't get enough clues to know for sure.
The lack of information in 'Pulp Fiction' about the book Vincent is reading makes it impossible to give a proper description. We can only assume that it might be something in line with the dark and gritty world of the movie. It could potentially be a crime or mystery novel, given the nature of the story and the character of Vincent. But really, this is just baseless speculation as the movie gives us no real clues.