Trainee, irritated about poor payment initially, acquires some craftsmanship... He learns on the job (10)
I believe the answer is:
apprentice
'trainee' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for apprentice that I've seen before include "Learner" , "new worker" , "Trainee" , "student" , "Novice" .)