Have a quick question about baggage allowance on a DONE :

HKG-xFRA(CX)-xLHR-NCL(BA) / NCL-LHR (BA) / LHR-GIB (BA) // LHR-ORD (AA) / ORD-xBOS-HKG (CX)

I am only concerned about the first leg. CX J limit is 30kg.

Wiki says 2 pieces, with weight limits per piece with different airlines.

Which applies? If its the piece rule, what is the limit per piece? Would the dominant carrier rule apply and if so, how?

Thanks in advance.