America again exposed monstrous European citizen (8)
I believe the answer is:
athenian
'citizen' is the definition.
(I have seen 'European citizen' mean 'athenian' so perhaps 'citizen' could also mean 'athenian')
'america again exposed monstrous european' is the wordplay.
'america' becomes 'A' (common abbreviation - e.g. in organisation names).
'again' becomes 'then' (I've seen this before).
'exposed monstrous european' becomes 'ian' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'then'+'ian'='ATHENIAN'
Can you help me to learn more?
(Other definitions for athenian that I've seen before include "Native of Grecian capital" , "Citizen of capital of Hellas" , "Citizen of Greece's capital" , "of capital city" , "Native of Greek capital" .)