Display of slippers rocks head office in Cornwall? (3,4)
I believe the answer is:
ice show
'display of slippers' is the definition.
(display of people slipping around on ice)
'rocks head office in cornwall?' is the wordplay.
'rocks' becomes 'ice' (both can informally mean diamonds).
'head office' becomes 'HO'.
'in' means one lot of letters goes inside another.
'cornwall?' becomes 'SW' (Cornwall is in the South West of England).
'ho' inserted within 'sw' is 'show'.
'ice'+'show'='ICE-SHOW'
(Other definitions for ice show that I've seen before include "winter spectacular?" , "Skating event" , "exhibition" , "Skating entertainment" , "form of entertainment" .)