Claim to be all on edge without Don (6)
I believe the answer is:
allege
'claim' is the definition.
(I've seen this before)
'all on edge without don' is the wordplay.
'without' is a deletion indicator.
'on'+'edge'='onedge'
'onedge' with 'don' taken away is 'ege'.
'all'+'ege'='ALLEGE'
'to be' acts as a link.
(Other definitions for allege that I've seen before include "Make a claim without proof" , "State as a fact without proof" , "Accuse without established proof" , "Swear" , "Claim (a person is guilty)" .)