To answer the original question: Yes, screenshots for both "iPad Pro (12.9-inch) (2nd generation)" and "iPad Pro (12.9-inch) (3rd generation)" are required.
Xcode 11 by default only includes a simulator for "iPad Pro (12.9-inch) (3rd generation)", but you can install a simulator for "iPad Pro (12.9-inch) (2nd generation)":
- Open Xcode
- Window > Devices and Simulators
- Select Simulators tab. The list of your current siumulators should appear in the the left sidebar of the window.
- Click the "+" at the bottom of the sidebar. The "Create a new simulator" sheet should appear.
- Click the Device Type menu and select "iPad Pro (12.9-inch) (2nd generation)"
- Click Create
Then you can create screenshots for the "iPad Pro (12.9-inch) (2nd generation)" using your new old simulator.