In some iPad apps—including Mail, Notes, Safari, and Files—you can have multiple windows open, and you can view all the open windows for an app at once, including those in Split View and Slide Over.
Do any of the following:
Swipe up from the bottom edge of the screen to reveal the Dock.
Go to the Home Screen.
Touch and hold the app whose windows you want to view, then tap Show All Windows.
Note: If you touch and hold an app for too long, all of the apps begin to jiggle. Tap Done or press the Home button (on an iPad with a Home button), then try again.
The open windows in some apps appear as thumbnails near the bottom of the screen. When you tap a thumbnail, its contents appear in the current full-screen window. When viewing apps in Split View, tap to open a new window.