The admin/author has added a job aid to the course but when viewed as a learner under Certification (which is how learners take the course), they cannot see the job aid.

The job aids are visible when the learner clicks on the course. It will not be visible on the main page of the certification. Please find the below :

Since the job aids are tagged at the course level, when the learner clicks on the course inside the certification, job aids will be visible.