Under discussion in answer paper (2,5)
I believe the answer is:
at issue
'under discussion' is the definition.
(I've seen this before)
'answer paper' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'paper' becomes 'tissue' (tissue is a kind of paper).
'a'+'tissue'='AT ISSUE'
'in' acts as a link.
(Other definitions for at issue that I've seen before include "Being discussed or disputed" , "Questionable" , "In question, under discussion" , "under debate" , "in dispute" .)