Mathematician docked in Italian city (5)
I believe the answer is:
turin
'italian city' is the definition.
(I've seen this in another clue)
'mathematician docked' is the wordplay.
'mathematician' becomes 'turing' (Alan Turing).
'docked' means to remove the last letter (to dock can mean to remove the tail of an animal).
'turing' with its last letter taken off is 'TURIN'.
'in' acts as a link.
(Other definitions for turin that I've seen before include "14 Italian city" , "First capital of a united Italy, 1861-65" , "Italian city with famous religious Shroud" , "regional capital" , "It. city housing shroud" .)