The easiest way is to install a bleeder fitting up at the clutch master cylinder since any air bubbles in the system will rise to the highest point. Why Ducati put the bleed valve at the system low point I’ll never understand.
If you can't find one, you can try just loosening the bolt slightly and bleed air from the banjo bolt as if it were a bleeder fitting.
Be careful to avoid spraying the hydraulic fluid. Keep plenty of rags handy to clean up any spills and cover everything. The fluid is corrosive and will damage painted surfaces and certain plastics.