Encourage in doubtful behaviour, eg go nude first! (3,2)
I believe the answer is:
egg on
'encourage' is the definition.
(to egg somebody on is to encourage them)
'doubtful behaviour eg go nude first' is the wordplay.
I cannot really see how this works, but
'eg' is present in the answer.
'go' is within the answer.
'nude first' could be 'n' (1st letter of 'nude') and 'n' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for egg on that I've seen before include "Urge (someone) to take risks" , "Prompt" , "Soldier may have this" , "this face is obvious embarrassment" , "Fire" .)