If you create a new quiz through an assignment group and do not add quiz questions, the quiz will be worth zero points in the Gradebook. This may be because the quiz has no questions, so you need to add questions to the quiz before students take the quiz in Canvas. If the quiz was taken outside of Canvas, you have to create an assignment using the No Submission submission type. To display points possible for the quiz, add quiz questions to the quiz. Otherwise, you can change the assignment type to something else, such as No Submission or On Paper.