Pulling a face off the top of one's head can be revealing (6)
I believe the answer is:
outing
'revealing' is the definition.
(outing is a kind of revealing)
'pulling a face off the top of one's head' is the wordplay.
I cannot really see how this works, but
'off' could be 'out' and 'out' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This may be the basis of clue (or it may be nonsense).
'can be' is the link.
Can you help me to learn more?
(Other definitions for outing that I've seen before include "Excursion as for picnic" , "Revealing orientation" , "Day excursion" , "Day trip" , "Excursion, trip" .)