Book fair welcomed by additional quarter of European city (10)
I believe the answer is:
montmartre
'quarter of european city' is the definition.
'montmartre' can be an answer for 'quarter' (I have seen 'painterly quarter' mean 'montmartre' so perhaps 'quarter' could also mean 'montmartre'). I am unsure of the 'of european city' bit.
'book fair welcomed by additional' is the wordplay.
I cannot really see how this works, but
'book' could be 'nt' (New Testament) and 'nt' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for montmartre that I've seen before include "sort of square where artists met" , "Parisian location" , "bohemian district" , "painterly quarter" , "District of Paris, associated with many artists" .)