Coolness of pal mob troubled (6)
I believe the answer is:
aplomb
'coolness' is the definition.
(thesaurus)
'pal mob troubled' is the wordplay.
'troubled' indicates anagramming the letters.
'pal'+'mob'='palmob'
'palmob' with letters rearranged gives 'APLOMB'.
'of' acts as a link.
(Other definitions for aplomb that I've seen before include "Self-confidence, assurance" , "Self-satisfied assurance" , "Self-satisfied dignity, complacency" , "Self-possession - coolness" , "coolness is required" .)