Studies grasses when speaking (5)
I believe the answer is:
reads
'studies' is the definition.
('read' can be a synonym of 'study')
'grasses when speaking' is the wordplay.
'grasses' becomes 'reeds' (type of grass plant).
'when speaking' indicates a 'sounds like' (homophone) clue.
'reeds' is a homophone of 'READS'.
(Other definitions for reads that I've seen before include "Peruses" , "Studies (at university)" , "Understands written language" , "Scans" , "Looks at and undertsands the written word" .)