Site Admins can assign another user only to a Job Admin level which does not include any permissions the Site Admin does not have themselves. If a Job Admin level includes one or more permissions the Site Admin does not have, the Site Admin will not see that Job Admin level available when assigning job-based permissions to Job Admin / Interviewer users.
Example: A Site Admin who lacks the user-specific permission Can see private notes, salary info, manage offers, request approval, and approve jobs/offers cannot assign another user to a Job Admin level which includes the Can see private notes, salary info, manage offers, request approval, and approve jobs/offers permission stripe (such as the default Job Admin: Private level).
To learn how to check your own user permissions, please see the following Help Center article: View Permissions on Personal User Account