Cathay generally reserve some seats for their own members. I am not aware of waitlist function via Qantas FF. There are paid services such as Expertflyer that provide some sort of notification for more award seats being made available.
Cathay has a tendency of releasing more award space closer to the departure date. However, best to make some backup plans in case this doesn’t eventuate.
If seats are not available on Asia Miles, you could waitlist via Asia Miles and I have had experiences where AM waitlist cleared and there was availability through Qantas too.
As mentioned, Cathay typically opens up a lot of award seats closer to departure. I can’t remember the details, but I think it’s every seat in business class except for one or two, and that this was released maybe 48-72 hours before departure. So it’s great for last minute or impulsive trips, but not so useful if trying to plan something specific in advance.