Journalist on the subject of drink (8)
I believe the answer is:
reporter
'journalist' is the definition.
(thesaurus)
'on the subject of drink' is the wordplay.
'on' is a charade indicator (letters next to each other).
'the subject of' becomes 're' (I've seen this in other clues).
'drink' becomes 'porter' (porter is a kind of drink**).
're'+'porter' is 'REPORTER'.
(Other definitions for reporter that I've seen before include "One may write a column" , "Newspaper writer" , "Newsperson" , "News person" , "He gives details" .)