Double in Hanover, in Germany (6)
I believe the answer is:
ringer
'double' is the definition.
(I know that ringer is a type of double)
'in hanover in germany' is the wordplay.
'in' indicates a hidden word.
'RINGER' is hidden in the letters of 'hanover in germany'.
(Other definitions for ringer that I've seen before include "Campanologist's" , "One is almost identical to another in the belfry" , "Lookalike" , "someone who shouldn't be competing?" , "Doppelganger" .)