Letter on where to drink beer (5)
I believe the answer is:
aleph
'letter' is the definition.
(letter of the Hebrew alphabet)
'on where to drink beer' is the wordplay.
'on' means one lot of letters go next to another.
'where to drink' becomes 'ph' (abbreviation for public house, a pub).
'beer' becomes 'ale' (I've seen this before).
'ph' after 'ale' is 'ALEPH'.
(Other definitions for aleph that I've seen before include "Hebrew character" , "First character" , "Sign of a beast? A Phoenician" , "Abroad, a" , "letter in Middle East" .)