At which horses display a range of skills (8)
I believe the answer is:
gymkhana
'at which horses display a range of skills' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gymkhana that I've seen before include "Event for horse-riders" , "Meet at which riders and horses display skills" , "Field day for equestrians" , "Equestrian games" , "A horsey 28" .)