At barbie, Jack becomes mine (8)
I believe the answer is:
turnspit
'at barbie jack' is the definition.
I can't tell whether this definition defines the answer.
'becomes mine' is the wordplay.
'becomes' becomes 'turns' ('turn' can be a synonym of 'become').
'mine' becomes 'pit' (down the pit).
'turns'+'pit'='TURNSPIT'
Can you help me to learn more?
(Other definitions for turnspit that I've seen before include "old servant who cooks" , "Lowly servant" , "Old roast attendant" , "Cooking assistant" , "You have rotisserie" .)