About to do karaoke cover? (6)
I believe the answer is:
casing
'cover?' is the definition.
(I have seen 'Outside cover ' mean 'casing' so perhaps 'cover' could also mean 'casing')
'about to do karaoke' is the wordplay.
'about' becomes 'ca' (abbreviation for 'circa').
'to do karaoke' becomes 'sing'.
'ca'+'sing'='CASING'
(Other definitions for casing that I've seen before include "Protective covering as of engine" , "Outer protective covering" , "Outside cover" , "This gives protection" , "Outer covering of something" .)