Firstly, you have to have all ATPL subjects from an ICAO state.
Cathay use a points based system for applicants. Points are gained by having, a Multi Rating, Turbine Rating, Jet Rating, Hours, etc.
eg. One person may get an interview with 1300 hrs TT and multi piston time, where as the next person may have 4000 hrs TT with Turbine command time.
Cathay have always liked to interview a broad cross-section of applicants.
So, your priority has to be, get those ATPL subjects. Then write and ask for a apllication form. Follow this up with a phone call. Update and ring regularly.
It is an advantage to have an ATPL licence when you come to Hong Kong. This could save you doing more exams later on. But it is not essential.
Good luck.