We have several communication channels that we actively support, each for different purposes.
Filing Bugs and Feature Requests
If you have identified a bug in Cobalt common code - meaning that you don't expect that it is related to a platform or port implementation quirk, then you should file a bug on our public issue tracker.
Additionally, if you have specific feature requests, you can also file them on our public tracker, but they should be very concrete and well-specified. If unsure, ask about your request on cobalt-dev first.
You will need a valid Google account to post. You can create a Google account with a non-gmail address (say, your work email address).
We also encourage contributions by sending pull requests on Github, especially if the bugfix or feature addition is small, well tested, and follows our contribution guidelines.
Asking about Schedules, Discussing Features, Announcements, and Miscellany
We also have a dedicated mailing list, cobalt-dev@googlegroups.com. If you are spending time with Cobalt, you may want to subscribe. And if you have a concern that doesn't fit into the above categories, asking about it on cobalt-dev is a reasonable course of action.
Use this mailing list for asking related technical questions about Starboard or Cobalt. We encourage searching through archives both in mailing list and bug tracker for prior questions.
If your issue seems like a bug or is really a feature request, use the Issue Tracker to file it.
YouTube Topics
If you are using Cobalt for YouTube on your device, and have YouTube-specific questions, you should contact your YouTube technical account manager directly. The above forums are Cobalt-specific, but not YouTube-specific. The Cobalt engineering team can't speak on behalf of Google or YouTube.