How did you purchase the ticket? Is it CZ ticket stock? Were the flights ticketed as codeshares?

Are you able to find the reservation on the CZ website? Have you tried finding your details on the Saudia Airlines website using your name and the ticket number? [It sounds crazy, but the Saudia website works surprisingly well to check tickets and reservations, especially for SkyTeam carriers, especially when you don't know the PNR for your reservation in the system of the airline that operates your flight.]

I don't know the CZ rules, but it might be the case that seats can only be reserved approximately 90 days before the flight; that's a common rule. Also, are you in coach? If so, have you checked whether CZ assigns coach seats before check in? This information should be on their website.

Even if you didn't care about the seat assignments, if you suspect that ther might be a problem with your ticket or reservation, try to phone the operating carrier to check whether they see a confirmed reservation with a matching ticket. Always travel with a hard copy of your ticket receipt (with ticket number) and reservation (showing PNRs of all carriers) or at least make sure that you ahve these numbers with you in case of problems.

You will probably eventually need to see an agent to check in so that visa requirements can be verified. My guess [be sure to check carefully] is that you won't need a visa for China transit (unless you're spending time in China as a stopover in either direction) but you may need an ETA in advance for Australia.