Golden Temple or Sri Harmandir Sahib
One word my city, it ends with a king;
Amritsar ends with 'tsar' which means emperor of Russia.
(I'm sorry for not noticing the letter 't' and thanks @M Oehm for pointing it out)
two words my own name, a mecca with bling.
The name is two word, Golden Temple, and it's a heart of the Sikh just like mecca is to Islam. That brings us to, Mecca(temple) with a bling(golden).
Three old trees decorate my hallowed doors,
This refers to three Ber trees near the hollowed entrance of the the two storey courtyard. (Ber Baba Buddha, Laachi Ber and Dukh Bhanjani Ber)
four walls of aurum, a pool and two floors.
In that order, the golden temple itself, the sacred pool, and the two storey courtyard. (Aurum is Latin for 'gold').
Five times nine decades since I came to be;
The construction started in 1581.
six are the people who venerate me.
It is the holiest and the most important pilgrimage site of Sikhism. Six is a wordplay on 'Sikh'.