The room of requirement or the divination tower
It did not matter where it was, it was on the same floor so the Ravenclaw did not need to search for long. He had been in the room once before and when he found it, he used the password and entered.

He walked forward towards where the Professor was seated. Said a quick hello and then turned to sit at one of the tables. Taking a seat near the middle . It was always the middle now he thought about it.... he then pulled out a new book, a crime book this time instead of a textbook and continued to read before the professor started the lesson.