I am Zimraan from Pakistan. I have a girl friend in HK. We wish to get marriage. How can I get visa

Zimraan, you can just apply for a HK visit entry permit to enter HK and then marry her.
You first need to prepare the following documents including your passport and copy of its data page, the completed application form attached with a recently-taken passport-sized color photo, your financial support proof, flight itinerary and travel plan to HK. And then ask your girlfriend to submit your application to HK immigration department to apply for the entry permit.