Diamonds, together with collar, falling from the top (8)
I believe the answer is:
dandruff
'falling from the top' is the definition.
(dead skin from the head)
'diamonds together with collar' is the wordplay.
'diamonds' becomes 'd' (abbreviation for the card suit diamonds).
'together with' becomes 'and' (I've seen this before).
'collar' becomes 'ruff' (ruff is a kind of collar).
'd'+'and'+'ruff'='DANDRUFF'
(Other definitions for dandruff that I've seen before include "Hair affliction" , "Unsightly scalp scurf seen on clothes" , "Flecks" , "shedding scales" , "Unsightly flakes falling from scalp" .)