Clock surmounting management’s information site (11)
I believe the answer is:
noticeboard
'information site' is the definition.
(board with information on it)
'clock surmounting management's' is the wordplay.
'clock' becomes 'notice' (clock can mean to notice or spot).
'surmounting' is a charade indicator (letters next to each other) (in a down clue, some letters go on top of others).
'management' becomes 'board' (eg the board managing a business).
'notice'+'board'='NOTICEBOARD'
(Another definition for noticeboard that I've seen is " that displays information".)