Number taking part in Pygmalion, in earnest (4)
I believe the answer is:
nine
'number' is the definition.
(nine is a number)
'part in pygmalion in earnest' is the wordplay.
'part' indicates the answer is hidden within the clue.
'NINE' is hidden within 'in pygmalion in earnest'.
'taking' is the link.
(Other definitions for nine that I've seen before include "One more than fourteen across" , "Number IX" , "Days Lady Jane 5 ac reigned" , "Cat's lives? - the next clue?" , "A number of worthies" .)