Apple today seeded the first beta of an upcoming macOS Mojave 10.14.2 update to its public beta testing group, two days after seeding the beta to developers and a few days after releasing macOS Mojave 10.14.1.
We don't know what improvements the second update to macOS Mojave might bring, but it is likely to include performance improvements and bug fixes for issues that weren't able to be addressed in the macOS 10.14.1 update.
Nothing new was discovered in the macOS Mojave 10.14.2 update provided to developers, so this software may be focused on under-the-hood changes that might not be discovered until it's released. Apple's release notes only mention an upcoming change requiring TLS certificates issued after October 15 to meet Apple's Certificate Transparency policy.
macOS 10.14.2 requires that publicly-trusted Transport Layer Security (TLS) server authentication certificates issued after October 15, 2018 meet the Certificate Transparency policy to be evaluated as trusted on Apple platforms.
macOS 10.14.2 follows macOS 10.14.1, an update that introduced Group FaceTime support for chatting with up to 32 people at one time and new emoji characters.