When I select a Callout within my 3D Model the Callout highlights, but the actual Clip Volume itself with the green Cut Plane handle and four outer blue Edit handles does not display.
Check whether the Disable Handles icon is depressed in the Element Selection tool.
If it is, click the icon to uncheck it since this option will prevent the Clip Volume from displaying (as well as the small, blue rectangular Edit Handles on other objects).