Piano, one in jazzy club known to all (6)
I believe the answer is:
public
'known to all' is the definition.
'piano one in jazzy club' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'jazzy' indicates anagramming the letters.
'club' is an anagram of 'ublc'.
'i' going inside 'ublc' is 'ublic'.
'p'+'ublic'='PUBLIC'
(Other definitions for public that I've seen before include "School or house" , "People in general" , "General - population" , "Relating to the general community" , "Offence against common decency" .)