Have you prepared the chart already? Are you showing anything in the chart? If so - when the user selects something from the menu - you will need to prepare the new items source for the chart and then pass it to the ItemsSource property.
The full source code for the RadDomainDataSource sample can be found under your local installation path. For example - C:\Program Files (x86)\Telerik\RadControls for Silverlight Q1 2012\Demos.
Feel free to contact us again if you have any specific questions.
All the best,
the Telerik team
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