One who kills a couple of donkeys at home? (8)
I believe the answer is:
assassin
'one who kills' is the definition.
'a couple of donkeys at home?' is the wordplay.
'a couple of donkeys' can mean two substitutions for 'donkey'.
'donkey' becomes 'ass' (I've seen this before).
'donkey' becomes 'ass' (I've seen this before).
'at home?' becomes 'in' ('in' can be similar in meaning to 'at home').
'ass'+'ass'+'in'='ASSASSIN'
(Other definitions for assassin that I've seen before include "I kill" , "butcher" , "Killer of prominent figure" , "Hired murderer" , "Hired killer" .)