How to check which airline allows stopovers when using Alaska Miles to fly between Australia and the US?

I am planning on buying points on Alaska Airlines to fly between Australia and the US. I understand a stopover may be allowed on one way awards by certain airlines. I’m seeking advice on how to select the airlines which allow stopovers (Qantas seems to auto select and I can’t see where they allow stopovers, and then I can’t see how to deselect them and select others), and where on the booking screen stopovers can be selected instead of the direct flight.

I think it depends where are you flying.

Korean don’t allow one way awards, and I don’t think Delta flies to anywhere but Sydney in Australia.

This leaves you CX, QF and Fiji Airways. From my experience all have pretty limited availability. Try breaking down your journey into segments (for example if you want to fly MEL - NYC via HKG, try first searching for MEL - HKG, then HKG - NYC) using the multi-city option.