Partial Region Screenshots on iPad pro connected to an external display

By far the easiest method to trigger and save a screenshot is to set-up and use the corner-swipe gesture.

• Open the Settings app on your iPad
• Go to the General menu and then choose the Gestures option
• Make sure “Allow Finger to Swipe From Corner” is enabled
• Choose the action you want (Screenshot) when swiping from either (or both) the left and right corners

Now that you have enabled the corner swipe, you can easily capture a screenshot with just your finger (or Apple Pencil). Just swipe diagonally from the lower-left or lower-right corner of the screen towards the centre; this will immediately trigger the screenshot.

The other ways to trigger a screenshot from an iPad are described here:

Take a screenshot on your iPad - Apple Support

By definition, a screenshot will capture the entire screen. If you only wish to capture part of the screen, you’ll need to crop the captured image using the markup tools:

Take and mark up a screenshot with Apple Pencil on iPad - Apple Support