You cannot link quiz questions to a competency. You can link a quiz activity - with a "rule" when the competency will be awarded.
If you have a set of questions that would award competency #1 and another set of questions that would award competency #2 - your options are two quizzes each quiz award the specific competency. Or if the students completes the quiz that is not randomized that has both sets of questions - and achieves the passing conditions is awarded the competencies.
Kind Regards.