The first beta version of iOS 9.2.1 was released on December 16. For now, almost three weeks later, Apple has released the second version of tests for developers and beta testers.
The 13D14 build is available for download both on the Apple developer portal and on iOS itself (as long as you are running beta versions on your iGadget) including for those who are part of the Apple Beta Software Program.
As in the first beta, for now we have no information about the focus of this update, but if something comes up we will let you know here on the site. Either way, you shouldn't expect anything but bug fixes and general improvements.