Damning evidence dodgy US monk’s smuggling in goods (7,3)
I believe the answer is:
smoking gun
'damning evidence' is the definition.
(I've seen this in another clue)
'dodgy us monk's smuggling in goods' is the wordplay.
'dodgy' is an anagram indicator (a dodgy or wrong order of the letters).
'smuggling' means one lot of letters goes inside another (some letters smuggled inside).
'goods' becomes 'gg' (an abbreviation for 'good' repeated).
'us'+'monk'='usmonk'
'usmonk' anagrammed gives 'smokun'.
'in'+'gg'='ingg'
'smokun' going around 'ingg' is 'SMOKING GUN'.
(Other definitions for smoking gun that I've seen before include "Weapon evidently just used" , "Unarguable evidence" , "Convincing evidence" , "Immediate and irrefutable evidence of crime" , "Clear evidence" .)