Where should I go to renewal HKSAR passport?

You need to go to the nearest Chinese consulate to submit your renewal. It takes 4 to 8 weeks because your application will be sent to HK Immigration Department. I don't think you have enough time to do this. Here are another two solutions: If you hold new HK ID card, you can apply for the people's Republic of China Travel Permit and then go back to HK with it. If you hold old ID card, you should apply for the Declaration of Identity for Entry Purposes.