is an event and not a command -- you can hook up an event handler to it, but you cannot bind a command.
Generally the current version of RadChart does not provide support for ItemClick commanding but we will be introducing ChartArea.Command / CommandParameter
properties for the official Q3 2010 SP1 release (around mid-January) and then you will be able to achieve the desired functionality.
You can also preview the commanding functionality by downloading the weekly internal build from your Client.Net account right now.
the Telerik team
Browse the videos here>>
to help you get started with RadControls for Silverlight