Nancy, you, Grant, John? (6)
I believe the answer is:
toilet
'john?' is the definition.
(I know that toilet is a type of john)
'nancy you grant' is the wordplay.
'nancy you' becomes 'toi' (I am not sure about this - if you are sure you should believe this answer much more).
'grant' becomes 'let' (I've seen this in another clue).
'toi'+'let'='TOILET'
Can you help me to learn more?
(Other definitions for toilet that I've seen before include "Plumbing fixture" , "where penny the cost?" , "Smallest room" , "Lavatory paper" , "It means washing" .)