Agree to study a dog (6)
I believe the answer is:
concur
'agree' is the definition.
(I know that agree can be written as concur)
'study a dog' is the wordplay.
'study' becomes 'con' (con can mean to study).
'a dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'con'+'cur'='CONCUR'
'to' is the link.
(Other definitions for concur that I've seen before include "Agree, assent" , "share the same opinion" , "Give assent" , "Be in accord" , "meet" .)