Exemplary piece of instruction (6,6)
I believe the answer is:
object lesson
'instruction' is the definition.
(thesaurus)
'exemplary piece' is the wordplay.
I cannot quite understand how this works, but
'piece' could be 'lesson' (I have seen 'Piece of instruction' mean 'lesson' so perhaps 'piece' could also mean 'lesson') and 'lesson' is found within the answer.
The remaining letters 'object' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for object lesson that I've seen before include "Example typifying a principle" , "punishment intended as a warning to others?" , "What may be striking" , "shows what one should do" , "Instructive experience" .)