The answer, once again, is to do your job (5)
I believe the answer is:
reply
'the answer' is the definition.
('reply' can be a synonym of 'answer')
'once again is to do your job' is the wordplay.
I cannot really understand how this works, but
'again' could be 're' and 're' is present in the answer.
'do' could be 'ply' (plying is a kind of doing) and 'ply' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for reply that I've seen before include "Return" , "Retort" , "Comeback" , "Come back" , "acknowledgement" .)