Observing or taking down (6)
I believe the answer is:
noting
This clue is a double definition.
'observing' is the first definition.
(note can mean to observe or notice)
'taking down' is the second definition.
('note' can be a synonym of 'take down')
(Other definitions for noting that I've seen before include "Observing and jotting down" , "Recording in writing" , "Paying close attention to something" , "Making brief record as memory aid" , "Making brief record of something" .)