Of which, the mayor may have a chain (6)
I believe the answer is:
office
This clue could be a double definition.
'of which the mayor' is the first definition.
The definition suggests a singular noun which matches the answer.
'a chain' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'may have' acts as a link.
Can you help me to learn more?
(Other definitions for office that I've seen before include "Business room or religious rite" , "Professional or clerical duties are performed here" , "Workplace for clerks" , "Workplace for white-collar workers" , "Business premises" .)