When you move an object (a layer, group, camera, or light) in a 3D project, an inset view appears in the lower-right corner of the Canvas, showing the scene from a different camera’s point of view. If you’re viewing the scene through the active camera, the inset view shows the Perspective camera’s point of view. If you’re viewing the scene through any other camera, the inset view shows the active camera. Use the inset view to see the results of changes that you make in orthogonal views.
Show the inset view
Click the View pop-up menu above the Canvas, then choose Show 3D Overlays and Inset View.
A checkmark next to an overlay type in the pop-up menu indicates that the overlay is enabled in the Canvas.
You can set the inset view’s size and when it appears in the Canvas by opening Motion Preferences (press Command-Comma), then adjusting the settings in the 3D pane.