It seems that the official Vulkan support has been released. But I cannot find the example page about how to use it? I thought it must be quite different from GLUT example since the verbosity of Vulkan.

The road map page shows Vulkan finished up. https://www.noesisengine.com/bugs/view.php?id=1820

Yes, the implementation is finished and internally being tested by a few clients. We plan to release this officially with 3.2. First beta (including Vulkan) is planned to be released "soon" : )

How to participant in beta test? The information about the beta test is usually hid somewhere or I can find it at a prominent place?

Yes, in the Official Announcements