A piece of learning (5)
I believe the answer is:
study
I believe this clue is a double definition.
'a piece' is the first definition.
(study is a kind of piece)
'learning' is the second definition.
(study is a kind of learning)
'of' is the link.
(Other definitions for study that I've seen before include "Examine carefully" , "Scrutinise" , "Room for work/reading" , "See 11" , "Analysis" .)