From the information provided I guess you want to have both XValue and YValue shown in a Tooltip . This can easily be done as shown in our Tooltip help topic. Note the way categories and values are displayed in a tooltip per item via binding to DataItem's Quarter and Profit properties.
If you like you may use our TrackBall feature instead. It can display a small popup, similar to the tooltip, in order to provide more detailed information about the closest points to the track ball line's cross section. For more information on how to use it , please review this help topic.
the Telerik team