The Literal control doesn't have any visual appearance on a Web Form but is used to insert literal text into a Web Form. For example if you examine the HTML dump of a page with the following code in it
<asp:Literal ID="lit1" runat="server">some text</asp:Literal>
you will notice that only the text is rendered on the page - that is why there is no tooltip. If you want to have a tooltip on the text, you need to wrap it in some container - DIV, or P for example, with the corresponding "title" property.
the Telerik team