The first thing that you do is ask him for his test score!
(just kidding!)
Some real things that can be looked at:
Appearance - uniform neat, shoes clean, etc.
Signals - arm straight, clear signals, good visible count, foul reporting is clear.
Movement on the court - is he moving to get good looks when necessary? going across the lane as lead when appropriate?
Court presence - does he appear confident and in control? does he looked relaxed on the court and not tense? strong whistle? Good communication and teamwork with partner?
Depending on how new the guy is, I wouldn't bombard him with all of this stuff at once. Maybe a few things that he can work on at a time.