Italian city where a drink served up (4)
I believe the answer is:
pisa
'italian city' is the definition.
(city in Italy)
'a drink served up' is the wordplay.
'drink' becomes 'sip' (sipping is a kind of drinking).
'served up' shows that the letters should be reversed in order (in a down clue, going upwards).
'a'+'sip'='asip'
'asip' written backwards gives 'PISA'.
'where' acts as a link.
(Other definitions for pisa that I've seen before include "much-visited city" , "Place with leaning tower" , "City in Tuscany" , "Location of leaning tower" , "City with listed building" .)