on-the-job learner (6)
I believe the answer is:
intern
'on-the-job learner' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for intern that I've seen before include "Imprison the young doctor without trial" , "Imprison (enemy aliens)" , "to keep under lock and key" , "Medical graduate trainee" , "Hospital doctor (US)" .)