Could you please tell me where and how can i apply for Hong Kong visa in Korea?

You need to apply from the Chinese embassy in South Korea or send your application to the HK Immigration Department. If your application is processed by the embassy, you need to wait for working days. If it is done by the HK Immigration Department, you need to wait four to six weeks. The address of HK Immigration Department is below:
Receipt and Despatch Unit
Hong Kong Immigration Department
2/F, Immigration Tower
7 Gloucester Road
Wan Chai, Hong Kong