Pub’s requirement for Guinness (3)
I believe the answer is:
inn
'pub's' is the definition.
(I've seen this before)
'requirement for guinness' is the wordplay.
'requirement for' indicates the answer is hidden within the clue (the answer is required to spell part of the clue).
'INN' is hidden in the letters of 'guinness'.
(Other definitions for inn that I've seen before include "English country pub" , "Jamaica, for one" , "Small hotel or country pub" , "Local" , "Hostelry, tavern" .)