. You didn't specify exactly what event do you want, but in general when using the TreeView's drag and drop, the events are raised on the TreeView that is the source of the drag, rather than the destination. So in your case you won't be able to use the built in events.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed