The new macOS High Sierra 10.14.2 beta can be downloaded through the Software Update mechanism in System Preferences after the proper profile has been installed from Apple's Developer Center.
We don't yet know what improvements the second update to macOS Mojave will bring, but it is likely to include bug fixes and performance improvements for issues that weren't able to be addressed in the macOS 10.14.1 update.
Should we discover anything new in the 10.14.2 beta, we'll update this post.
The new 10.14.2 software comes just a day after Apple released macOS 10.14.1, an update that brought support for Group FaceTime on the Mac and introduced new emoji characters.
Update: Apple has removed the macOS Mojave 10.14.2 developer beta from the Developer Center for unknown reasons.
Update 2: The macOS Mojave 10.14.2 developer beta is available for download again.