Surplus count maybe will show who is boss (8)
I believe the answer is:
overlord
'is boss' is the definition.
(I've seen this before)
'surplus count maybe' is the wordplay.
'surplus' becomes 'over' (I've seen this before).
'count maybe' becomes 'lord' (I can't justify this - if you can you should give a lot more credence to this answer).
'over'+'lord'='OVERLORD'
'will show who' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for overlord that I've seen before include "Supreme ruler" , "Ruler, D-day Operation" , "Old rover (anag.)" , "top man!" , "Feudal ruler" .)