as far as i know:
For other Oneworld Sapphire while traveling with CX, the maximum of free checked-in luggage allowance is capped at 2 pieces.
For Cathay Gold (equivalent to oneworld sapphire), diamond and other oneworld Emerald while traveling with CX, you always get extra one piece of luggage, meaning if the ticket has already 2 pieces of free check in luggage, you will get extra 1 piece (in total 3).