He will speak at, either before or after (6)
I believe the answer is:
orator
'he will speak' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'at either before or after' is the wordplay.
'either' becomes 'or' (I've seen this in another clue).
'before' says to put letters next to each other.
'after' is a charade indicator (letters next to each other).
'at' put after 'or' is 'orat'.
'orat'+'or'='ORATOR'
Can you help me to learn more?
(Other definitions for orator that I've seen before include "To roar at a speech-maker" , "Eloquent public speaker" , "He addresses" , "Rhetorician" , "One addressing" .)