Admit academic robe's no good at university (3,2)
I believe the answer is:
own up
'admit' is the definition.
(I've seen this before)
'academic robe's no good at university' is the wordplay.
'academic robe' becomes 'gown' (I've seen this before).
'no' suggests deleting specific letters.
'good' becomes 'g' (abbreviation).
'at university' becomes 'up'.
'gown' with 'g' taken away is 'own'.
'own'+'up'='OWN UP'
(Other definitions for own up that I've seen before include "be honest" , "Confess, admit guilt (3.2)" , "Confess, acknowledge fault" , "Accept responsibility" , "Come clean (about wrongdoing)" .)