“read someone like a book”别理解成“像读书一样看某人”，引申为很了解某人，清楚了解某人动机（思想等）。

【例句】
My teacher can read students like a book. He knows which students study, and which students don't.
我的老师对学生很了解，他知道哪些学生学习，哪些不学习。

It's very clever of them. They must have read me like a book.
他们非常聪明，他们很了解我在想什么。