Understands king snakes (6)
I believe the answer is:
grasps
'understands' is the definition.
(grasping is a kind of understanding)
'king snakes' is the wordplay.
'king' becomes 'gr'.
'snakes' becomes 'asps' (asp is a kind of snake).
'gr'+'asps'='GRASPS'
(Other definitions for grasps that I've seen before include "Understands" , "Grips" , "Takes firm grip of" , "Takes hold of firmly" , "Clutches" .)