Knowledgeable editor supports European coin (8)
I believe the answer is:
educated
'knowledgeable' is the definition.
('educated' can be similar in meaning to 'knowledgeable')
'editor supports european coin' is the wordplay.
'editor' becomes 'ed'.
'supports' says to put letters next to each other (bottom letters provide a support for the top ones).
'european' becomes 'e' (abbreviation e.g. EU).
'coin' becomes 'ducat' (ducat is a kind of coin**).
'e'+'ducat'='educat'
'ed' put after 'educat' is 'EDUCATED'.
(Other definitions for educated that I've seen before include "Schooled, trained" , "Trained; learned" , "Cultivated, knowledgeable" , "Schooled, enlightened" , "Well-read" .)