Importing and Exporting Individual Quizzes
Click 'More' under the gear menu in the source course.
Select 'Moodle XML format' and the category of questions (this should match the title of the quiz) you want to export and click 'Export questions to file'
If you get a popup after this step asking you what to do with the file, save it to your desktop (or a more secure spot if you prefer).
Navigate to the destination course, click the gear, and choose 'More' again.
Choose 'Moodle XML format', upload the file you just downloaded (it will start with the word 'questions'), and click 'Import'.
You should see confirmation of success.
You can also use this import option to import quizzes and questions from publisher materials like test banks.