Basic things really, balance, punch variety, athletic ability (speed, reflexes, power, etc.) footwork, basic skills, that type of stuff.

Its questionable to me if you should be looking for heart, chin, etc in a guy with less than 10 or maybe 15 fights, unless you've really matched him tough for a prospect. If he's gonna be a big time fighter for the most part he shouldn't be having to show his chin and recuperative powers against part time journeyman. Definitely not on a regular or semi-regular basis.

Once the prospect begins to step up a little and face gatekeeper types, veterans, other good young prospects then obviously its important to see if he can take a punch, if he can recover from being hurt, if he can recover from a loss.