Doubtful pawnbroker, right to ring American (7)
I believe the answer is:
unclear
'doubtful' is the definition.
(unclear can mean doubtful or vague)
'pawnbroker right to ring american' is the wordplay.
'pawnbroker' becomes 'uncle' (old-fashioned term for a pawnbroker).
'right' becomes 'r' (common abbreviation).
'to ring' means one lot of letters goes inside another.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'uncle'+'r'='uncler'
'uncler' placed around 'a' is 'UNCLEAR'.
(Other definitions for unclear that I've seen before include "Poorly described" , "An ulcer (anag)" , "Imprecise, hazy" , "Not transparent or free from doubt" , "Not easy to grasp" .)