Pupil to confess after bishop exploded (5,2)
I believe the answer is:
blown up
'exploded' is the definition.
(I've seen this before)
'pupil to confess after bishop' is the wordplay.
'pupil' becomes 'L' (as in a learner driver with L-plates on their car).
'to confess' becomes 'ownup' (I've seen this before).
'after' says to put letters next to each other.
'bishop' becomes 'B' (chess abbreviation).
'l'+'ownup'='lownup'
'lownup' put after 'b' is 'BLOWN-UP'.
(Other definitions for blown up that I've seen before include "Exploded" , "what the bigger picture is" .)