Although i have to agree with Richard on this one, if you really want to use one event handler for multiple dropdowns the simplest way would be to just check to which dropdown does the current item belong to, something like this:
sender, Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
I would like to also suggest taking a look at this help article
, related to RadControl Spy, to be able to see the internal structure of the controls, for easier and better understanding of the internals.
Hope this helps, if you have any other questions or comments, please let me know,