Parasites notice knight before publican (8)
I believe the answer is:
licensee
'publican' is the definition.
(I've seen this before)
'parasites notice knight before' is the wordplay.
'parasites' becomes 'lice' (lice are parasitic insects).
'notice' becomes 'see' (notice can mean to spot or see).
'knight' becomes 'n' (chess abbreviation).
'before' is a charade indicator (letters next to each other).
'see' after 'n' is 'nsee'.
'lice'+'nsee'='LICENSEE'
(Other definitions for licensee that I've seen before include "one allowed to serve" , "Person with official permit to sell, say, drink" , "One holds official permission" , "The one with the official permit" , "One authorised to sell alcohol" .)