Attaching Command to ScrollViewer.ScrollChanged of ListView
EventTrigger doesn't trigger for routed events. You can use the solution proposed in this articleto create a RoutedEventTrigger class and use it instead of EventTrigger.
I recommend a Behavior for this. If you don't have Blend, you'll need to get the Blend SDK. But once you have that, you can follow this tutorial to extend the behavior of the ScrollViewer.