Hat that’s key for Oscar in city (7)
I believe the answer is:
hamburg
'city' is the definition.
(Hamburg is an example)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for hamburg that I've seen before include "Port near the mouth of the Elbe" , "German state and largest port" , "German city-seaport on the Elbe" , "A meat dish named after the city" , "North German city" .)