Required German city to return milk to the French (9)
I believe the answer is:
essential
'required' is the definition.
(I've seen this in another clue)
'german city to return milk to the french' is the wordplay.
'german city' becomes 'essen' (city in Germany).
'to return' is a reversal indicator.
'milk' becomes 'it' (I am not sure about this - if you are sure you should believe this answer much more).
'to' says to put letters next to each other (I've seen this in other clues).
'the french' becomes 'la' (one of the French words for 'the').
'it' put after 'la' is 'lait'.
'lait' backwards is 'tial'.
'essen'+'tial'='ESSENTIAL'
Can you help me to learn more?
(Other definitions for essential that I've seen before include "as oil might be" , "Basic or necessary" , "absolutely neccessary?" , "must-have item" , "organic" .)