Leaving questions that could be best answered by those who should have learnt their lessons (4,5)
I believe the answer is:
exam paper
'those who should have learnt their lessons' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'leaving questions that could be best answered by' is the wordplay.
I cannot really see how this works, but
'questions' could be 'exam' (a set of questions) and 'exam' is present in the answer.
'best' could be 'a' and 'a' is found in the answer.
'by' could be 'per' (I've seen this in another clue) and 'per' is located in the answer.
A single letter 'p' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for exam paper that I've seen is " Students should read".)