Intelligence is something that Bookman helpers need to get better in their job and both Intelligence and Knowledge for scientists. The only way to gain it is to read books and go on missions and collect information. As everyone knows, there are tons of books, sorted by what they tell about. Whether it's about history, romance, mystery, tragedy, horror etc. That is why I will show you what exactly you'll gain from a book you've read.
History - 5-6 intelligence
Detective - 4-5 intelligence
Mystery - 4-5 intelligence
Adventure - 4 intelligence
Fantasy - 4 intelligence
Tragedy - 3 intelligence
Romance - 3 intelligence
Horror - 2 intelligence
For you to be approved that you've read a certain book, you will have to describe it as much as possible. Depending on how, what and how much you've written, you'll be given the intelligence and experience. You can't read a second book from the same category if you haven't read the other types. You have to admit it. It won't be fair to choose only historical books, just because you want more knowledge. Besides you character doesn't know that. He would like to have a variety of book categories and read what he likes.