Cleric in bother about religious instruction (6)
I believe the answer is:
priest
'cleric' is the definition.
(I know that cleric can be written as priest)
'bother about religious instruction' is the wordplay.
'bother' becomes 'pest' (I've seen this in another clue).
'about' is an insertion indicator.
'religious instruction' becomes 'RI' (abbreviation).
'pest' placed around 'ri' is 'PRIEST'.
'in' acts as a link.
(Other definitions for priest that I've seen before include "Professional woman perhaps" , "Religious functionary" , "Conductor of religious service" , "Minister of religion" , "with orders" .)