Separate mattress flipped with skill (4,5)
I believe the answer is:
tell apart
'separate' is the definition.
(I know that separate can be written as tell apart)
'mattress flipped with skill' is the wordplay.
'mattress' becomes 'pallet' (pallet is a kind of mattress).
'flipped' says the letters should be written in reverse.
'with' is a charade indicator (letters next to each other).
'skill' becomes 'art' (both can mean a talent).
'pallet' backwards is 'tellap'.
'tellap'+'art'='TELL APART'
(Other definitions for tell apart that I've seen before include "See difference between" , "Rattle pal about - distinguish one from the other" .)