Does he swear to be a good soldier? (7)
I believe the answer is:
trooper
'soldier?' is the definition.
(trooper is a kind of soldier)
'does he swear to be a good' is the wordplay.
I cannot quite see how this works, but
'a' could be 'per' and 'per' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for trooper that I've seen before include "Soldier, proverbial swearer" , "He swears" , "Cavalryman" , "ship" , "Private soldier" .)