Currently the lighter render options have some limitations, one of which is the tooltip, it is not going to show. You can consider using the trackball behavior instead, it has the same notion as the tooltip - it will display information about data points close to the mouse cursor.
If you must have a tooltip in your application - you can implement custom tooltip in code behind where you will need to find the data points underneath the mouse cursor and handle the visibility and position of the tooltip. I have attached a simple project to demonstrate both the trackball behavior and the custom tooltip. I hope this information helps.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.