How does Cobb ask his tutor for a bibliography?

Just asking.

Just politely ask the tutor for a bibliography.

Tutors will give more bibliographies, and tutors will generally recommend more than 30 books. After reading the exam, it's over. In case the school recommended by the teacher doesn't take the exam, it's better to have professional doctoral counseling or guidance from relevant institutions, which will be much better and avoid many detours.