The object list is a sidebar on the left side of the Keynote window that lists the objects for selected slides in the order they’re layered on a slide (known as the stack). You can select multiple slides to show objects for more than one slide at a time, then select, lock, or move objects in the list.
The object list is particularly useful for selecting an object that would otherwise be difficult to select because it’s layered below other objects or in a nested group.
To open the object list, click on the left side of the toolbar, then choose Show Object List. Keynote must be in Slide Only view or Navigator view in order to show the object list.