Where to spend a penny in French ground (5)
I believe the answer is:
floor
'ground' is the definition.
(floor is a kind of ground)
'where to spend a penny in french' is the wordplay.
'where to spend a penny' becomes 'loo' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'french' becomes 'fr' (abbreviation).
'loo' placed into 'fr' is 'FLOOR'.
Can you help me to learn more?
(Other definitions for floor that I've seen before include "Minimum level or sea bottom" , "Part of building" , "Lower limit" , "American's story" , "Storey of a building" .)