Critic (6)
'critic' is the definition.
(I know that reviewer is a type of critic)
This is the entire clue.
(Other definitions for reviewer that I've seen before include "Writer who reports and analyses" , "Critic" , "Writer of criticism" , "Writer who assesses the merits of a book, play etc." , "One should be critical" .)
'critic' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for censor that I've seen before include "State official who vets books etc for crones" , "Bowdlerise" , "Official banner of books, films etc" , "Wield a blue pencil" , "Check contents of letter, play etc with a view to deleting passages" .)
'critic' is the definition.
(someone who knocks or criticises things)
This is all the clue.
(Other definitions for knocker that I've seen before include "Door rapper" , "It bangs on a door" , "Hinged device on a door" , "Door banger -- detractor" , "Something on door; one continually finding fault" .)