I forgot what the MCT is between KA/CX and KA/CX in HKG. I think it is 50 min. If so, that is not a legal connection and you won't be able to check through to CX 797.

It is very usual for afternoon PVG flights to be delayed or cancelled. I would suggest you change the outbound flight to the next day, or even both flights to the next day and allow plenty of time (I would say three hours) for transit.