Skill in mounting shows — HMS Pinafore, for example? (10)
I believe the answer is:
stagecraft
'skill in mounting shows' is the definition.
(skill in staging plays)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for stagecraft that I've seen before include "What playwright has" , "capacity for top performance?" , "Art of boarding" .)