Transit visit to hong kong. how can I apply for the visa from here? how long will it take?

Diggu, you can visit Chinese embassy in South Korea and ask if you can apply there. If so, it takes four working days. If they don't accept your application, then you need to post your application to HK Immigration Department directly. It takes four to six weeks for them to deal with your application. The postal address is: Receipt and Despatch Sub-unit Hong Kong Immigration Department 2/F, Immigration Tower 7 Gloucester Road Wan Chai, Hong Kong