I'm Pakistani citizen but I'm staying in italy with my Italian wife.

Yes, I think you can apply from there. First, you can go to the embassy there and see whether the office accepts your application. If it doesn't, you need to send your application documents by yourself to Hong Kong Imigration Department. The postal address is:
Receipt and Despatch Sub-unit
Hong Kong Immigration Department
2/F, Immigration Tower
7 Gloucester Road
Wan Chai, Hong Kong