What did all the people do when Ezra opened the Book of the Law in their sight?

Answer: Stood up

Ezra was standing above all the people, and as he opened the book in full view of them, all the people stood up.

“Ezra opened the book in full view of all the people, since he was standing above them all, and as he opened it, all the people stood up.”— Nehemiah 8:5 (BSB)