You can use these steps to add random question(s) from any question bank category within your course.
NOTE: You should always create new questions within a question bank category prior to adding questions to your quiz.
Enter the Quiz.
Click Questions from the secondary navigation menu.
Select + a random question from the Add drop-down menu for the page where you want to add a new question
Select the question bank category that contains your questions from the drop-down menu.
Click the Apply filters button.
At the bottom, select the Number of random questions from the drop-down menu.
Click the Add Random Question button.
Repeat steps 3-5 as desired for each category you want to pull questions from.