EDUCATION

understand clearly what sb´s character is

 If you spend some time observing him, you'll be able to master all its particulars
and read him like a book -- not the Jane Austen novel you've been enjoying.  Google

He is usually quite open
and honest about things, so you should be able to read him like a book.  Google

 I can read him like a book and he can do the same
with me.  Google