Jack, who doffs his cap in church space (5)
I believe the answer is:
knave
'jack' is the definition.
(knave can mean a jack playing card)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for knave that I've seen before include "Jack - the cad!" , "Honour" , "A swindler" , "cheat of old" , "Rat" .)