Look at gym trick (6)
I believe the answer is:
peruse
'look at' is the definition.
(perusing is a kind of looking at)
'gym trick' is the wordplay.
'gym' becomes 'pe'.
'trick' becomes 'ruse' (I've seen this before).
'pe'+'ruse'='PERUSE'
(Other definitions for peruse that I've seen before include "Scrutinise" , "Read or study carefully" , "Scan carefully for rupees" , "Survey" , "Read attentively" .)