Group's article on World Health Organization (3,3)
I believe the answer is:
the who
'group's' is the definition.
The answer is an example.
'article on world health organization' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'on' is a charade indicator (letters next to each other).
'world health organization' becomes 'who' ('WHO' can be a synonym of 'world health organization').
'the'+'who'='THE WHO'
(Other definitions for the who that I've seen before include "60s rock group" , "Rock group (Tommy, My Generation)" , "Loud rock band" , "Pop group (Tommy, Quadrophenia)" , "British pop group" .)