Expert reassessing cobs is on the nose (9)
I believe the answer is:
proboscis
'the nose' is the definition.
(proboscis is a kind of nose)
'expert reassessing cobs is' is the wordplay.
'expert' becomes 'pro' (short for professional).
'reassessing' indicates anagramming the letters.
'cobs' is an anagram of 'bosc'.
'pro'+'bosc'+'is'='PROBOSCIS'
'on' acts as a link.
(Other definitions for proboscis that I've seen before include "Long nose" , "Feeding appendage of elephant, insect" , "Elephantine nose" , "Elephant's trunk" , "MONKEY" .)