According to Cathy rules, if you are not flying on that flight to, from, or via the USA, than you get 30kg in J class, regardless of how many bags you check in. Its a maximum of 30kg.

If that flight IS to, from or via the USA, then you get 2 x 32kg bags.

This is true on Cathy flights only, not if your itinerary is a OW itinerary.

On a DONE4, the OW WWW says "Two (2) pieces 32kg (70lbs) each piece with total dimensions 158cm (62ins) allowed for each piece."

There are a lot of exceptions to this rule though eg. If Econ ticket, and you have a BA segment, ALL flights are 23kg max bag.