I am Pakistani passport holder how can i get HK visa ?

Shaban, you go there for sightseeing purpose, right? If yes, you can apply for a tourist entry permit. The first thing is to prepare the needed documents containing copy of your passport, the application form, a half-length color photo, flight itinerary, hotel reservation and your travel plan.
After, you can ask your friend to submit the application to HK immigration department directly for you to apply it. Or you can submit the application to the embassy of PRC to apply.