The capital of Hong Kong is Hong Kong. An area of the city known as Victoria used to house the capital. It has since moved to a more central location within the city.
Hong Kong is an independent city-state of China. This means that it ultimately falls under Chinese rule, but for economic and trade purposes, and as part of the agreement that transferred rule of Hong Kong from the U.K. to China, it is somewhat self-governing. Ultimately, China is responsible for Hong Kong's defense and foreign affairs. Hong Kong maintains independence in all other areas of government. It also continues to maintain its own currency.