Well-known to involve secretary where comments may be made (7)
I believe the answer is:
notepad
'where comments may be made' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'well-known to involve secretary' is the wordplay.
'well known' becomes 'noted' (I've seen this before).
'to involve' is an insertion indicator (inserted letters get involved).
'secretary' becomes 'PA' (abbreviation for personal assistant).
'noted' enclosing 'pa' is 'NOTEPAD'.
Can you help me to learn more?
(Other definitions for notepad that I've seen before include "A secretary may have one" , "On which one writes" , "PC" , "writer's block" , "Block of writing paper; computer" .)