Feature of Copenhagen — Danish design kept secret (6,6)
I believe the answer is:
hidden agenda
'feature of copenhagen danish' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'design kept secret' is the wordplay.
I cannot really understand how this works, but
'design' could be 'end' (both can mean a purpose or goal) and 'end' is located in the answer.
'secret' could be 'hidden' (I've seen this before) and 'hidden' is present in the answer.
The remaining letters 'aga' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for hidden agenda that I've seen before include "Sub-text, unstated objective" , "Concealed intentions" , "Undisclosed reason" , "followed in secret meeting?" , "covert plan" .)