I am afraid a tooltip functionality is currently not supported by Kendo UI Radial Gauge, but we are planning to implement a static label for the pointer. We will appreciate if you share your idea with the tooltip as a feature request at our UserVoice page. This way the community would be able to vote for it and if this suggestion turns out to be popular we will consider its implementation.
the Telerik team
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI