There’s seven location in South Africa where you can take the HSK, YCT, BCT, or HSKK: Durban Institute of Technology, University of Cape Town, Cape Academy of Math, Science and Technology, Rhodes University, University of Stellenbosch, University of Johannesburg, and the Chinese Culture and International Education Exchange Center. Each of these locations has an official Confucius Institute, which is the only place you can take the official HSK test.
How to take the HSK
First, find which institution is closest or most convenient for you.
Then check the official test dates for the HSK and/or YCT and find the next available test. Expect to need to sign up about a month before you take the test. Also, make sure to call up the institution and double check that the exam hasn’t been canceled for some reason (I’ve gotten a couple reports of this happening and people were pretty upset).
Finally, sign up for the test online with the Confucius Institute headquarters in China called Hanban.