Could you please tell us how do you intend to show the ToolTips, when a tag is clicked or hovered? For your convenience I created a sample project, that loads RadToolTip when an item in the cloud is hovered. Note, that we need to set ID attribute to every element of the TagCloud so that we can determine for which tag the tooltip is loaded. Another thing that should be considered, is the RadToolTipManager should be placed after the TagCloud on the page, so that the IDs are set before the elements are tooltipified.
You can find the full source code attached to the thread.
the Telerik team