Hello Rainer,
The Kendo UI Menu's dataSource is not the Kendo UI dataSource that supports remote data operations and all the different events. The dataSource of the Kendo UI Menu is a simple array property. If you want to detect when the widget is initialized you can use the Angular kendoWidgetCreated event, as shown here:
http://docs.telerik.com/kendo-ui/AngularJS/global-events
Regards,
Kiril Nikolov
Telerik
Join us on our journey to create the world's most complete HTML 5 UI Framework -
download Kendo UI now!