Arising, well-groomed entertaining knight prepares for investiture (6)
I believe the answer is:
kneels
'prepares for investiture' is the definition.
'arising well-groomed entertaining knight' is the wordplay.
'arising' shows that the letters should be reversed in order.
'well groomed' becomes 'sleek' (I've seen this in another clue).
'entertaining' indicates putting letters inside.
'knight' becomes 'N' (chess abbreviation).
'sleek' going around 'n' is 'sleenk'.
'sleenk' backwards is 'KNEELS'.
(Other definitions for kneels that I've seen before include "Shows deference" , "Adopts customary position for prayer" , "Adopts normal posture for prayer" , "Genuflects" , "Awaits blessing" .)