Presumably one doesn't know when one does this (4)
I believe the answer is:
asks
'presumably one doesn't know' is the definition.
I can't tell whether this definition defines the answer.
'when one does this' is the wordplay.
I cannot really understand how this works, but
'when' could be 'as' (eg 'when I walked' means 'as I walked') and 'as' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for asks that I've seen before include "Inquiries" , "Questions" , "Begs" , "Enquires; requests" , "Inquires (4)" .)