Where, abroad, a piece of cake can take any form (5)
I believe the answer is:
kenya
'where abroad a piece' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'cake can take any form' is the wordplay.
'cake can' becomes 'ke' (I can't justify this - if you can you should believe this answer much more).
'take' says to put letters next to each other.
'form' is an anagram indicator (a different form of the same letters).
'any' is an anagram of 'nya'.
'ke'+'nya'='KENYA'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for kenya that I've seen before include "E African country" , "Republic in East Africa" , "Land" , "East African republic" , "East African country" .)