The Alaska award maps are here:
Mileage Plan airline miles award charts | Alaska Airlines
you are only permitted to fly from Asia to Australia on Cathay Pacific. And 'Asia' in this context = 'Hong Kong only'.
Cathay awards don't show on line with Alaska. You'd need to find availability via say the Qantas tool, or AA's tool, or even BA. And then call Alaska to book it for you.
however... (a) Alaska's availability doesn't necessarily match what you can find onany of those sites and (b) Cathay has married many of its award seats so that flying to or from Hong Kong only is difficult. Normally you have to fly beyond hong kong (two sectors, ie AU-HKG-xx_). So on a couple of fronts, if can be difficult to find CX availability via Alaska.
You might be able to find AU-HKG-USA. That is a married flight segment that will show on QF. But whether the availability can also be seen by Alaska you'd need to call and ask.