I am student in PR China from DR Congo and want to visit Hong Kong for two days only.

You need to have a Transit/Visit type to visit HK for only 2 days.
You can apply it by mailing all your documents to HK Immigration Department for applying directly. Your valid passport, an application form with a recent taken photo, your round trip tickets to HK, hotel booking, an bank statement (if any) are needed to prepare for application.

It is reminded that it takes around four weeks to get the permit, so you need to apply in advance.