Preview at WWDC likely in June, followed by September launch.
Apple Seeds Third OS X 10.11.2 El Capitan Beta to Developers
The new beta is available through the Software Update mechanism in the Mac App Store and can be downloaded through the Apple Developer Center.
We don't know exactly what improvements the second update to OS X El Capitan will introduce, as many of the changes seem to be under-the-hood upgrades. It’s likely to focus on bug fixes, security enhancements, and performance improvements to address problems that have popped up since the release of OS X 10.11.1.
Apple's release notes for OS X 10.11.2 have asked developers to focus on Networking, Graphics, Mail, Wi-Fi, Calendar, USB, Notes, Photos, and Spotlight.