Doctor and city tried to obtain proof of citizenship (8,4)
I believe the answer is:
identity card
'proof of citizenship' is the definition.
(type of identification)
'doctor and city tried' is the wordplay.
'doctor' indicates an anagram.
'and'+'city'+'tried'='andcitytried'
'andcitytried' with letters rearranged gives 'IDENTITY CARD'.
'to obtain' is the link.
(Other definitions for identity card that I've seen before include "personal document" , "Acidity trend (anag.)" , "credentials" .)