You can find the resource combobox in the advanced form by handling FormCreated as explained in this help topic - http://www.telerik.com/help/aspnet-ajax/scheduler-customizing-advanced-form-formcreated.html
->sroll down to the section on "Change the selected index of a resource combobox so always one option is preselected
". Then you can attach to its SelectedIndexChanged event dynamically.
I hope this helps.
the Telerik team
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