Depending on how a quiz is delivered to learners they may access it several ways.
Quizzes can be posted to Commuities and learners can access the quiz from the community in that case.
Quizzes can be attached to learning events as resources and learners can access quizzes from learning events.
Learners can also access quizzes through their user menu options.
Click the user's name in the top right.
Click on My Quizzes.