Cut off what dog wags? (7)
I believe the answer is:
curtail
'cut off' is the definition.
(thesaurus)
'dog wags?' is the wordplay.
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'wags?' becomes 'tail' (I can't justify this - if you can you should believe this answer much more).
'cur'+'tail'='CURTAIL'
'what' acts as a link.
Can you help me to learn more?
(Other definitions for curtail that I've seen before include "Shorten, abridge" , "Cut short (an activity)" , "Cut short like canine appendage" , "Reduce in extent" , "make shorter" .)