Assuming you're using Connect version 6 --
In the Quiz Manager, select the button "Edit Quiz Settings"
next to the quiz. From the drop-down list you can choose to make
the quiz optional, required, or pass required. This will apply to
the entire quiz, not just a single question within a quiz. If you
want to require some questions, but not others, put them in
separate quizzes.
Hope this helps.
Lisa