'Vacant' needed to follow punctuation mark in dictation (7)
I believe the answer is:
command
'dictation' is the definition.
(I know that dictation can be written as command)
'vacant needed to follow punctuation mark' is the wordplay.
'vacant' suggests removing the centre (a vacant or emptied out form of the word).
'to follow' means one lot of letters go next to another (some letters go after or follow others).
'punctuation mark' becomes 'comma' (comma is a kind of punctuation mark).
'needed' with its centre taken out is 'nd'.
'nd' put after 'comma' is 'COMMAND'.
'in' acts as a link.
(Other definitions for command that I've seen before include "Bidding" , "Authoritative order" , "Fiat" , "Instruction, order" , "Direct" .)