All Quiz Questions are stored in the Question Bank. If you want to reuse a question, it must be in a Category at the Top level of the Question Bank. (See Add Categories to the Question Bank.) You cannot reuse a question stored in a Default Quiz Category.
Note: If you use the same question in multiple quizzes, but want to modify the choices, wording, or order, make a copy of the question and modify it. (See Duplicate a Quiz Question.) Any changes to a question already in use in graded quizzes will affect the scoring in those quizzes. You will be warned to that effect when attempting to make a change.
Adding existing questions to your Quiz
When you add a question to a Quiz, you are linking to the question, not embedding it in the Quiz itself.
Go to the course homepage.
Find the quiz and click the quiz link..
Find the Administration block, Quiz Administration:
Click Edit quiz.
Click Add (far right menu link), then from question bank. You will see the TOP level categories under the Course Name.
Select the appropriate Top level category from the Select a category menu.
Check the checkbox for the question(s) you want to add to this quiz.
Click Add to quiz.
Click Save in upper-right corner, next to Maximum grade.