What particular aspects of the Prospector do you want to cover?
Andrew Leung has a number of photos on his website railgallery.info which show the Prospector in a number of locations.
Good photos of the train itself can be obtained from North of the line at Midland opposite the new hospital.
There are a number of sections of curved track between Toodyay and Avon Yard where good photos (and movie sequences) could be obtained. Andrew shows one of those, and shots at Midland. The road from Avon to Toodyay follows the line allowing a number of shots. Racecourse Road east of Toodyay might allow an elevated view of the curve there.
The Eastbound and Westbound morning Prospectors pass eachother at Merriden, and you could get photos and film of this. The train runs at 160km/h between stations in the wheat belt and a shot of this might be helpful.
There might be a good shot of the morning train from Perth arriving in Kalgoorlie from the footbridge at the station.