Commercial support for Jetty is available directly from the developers through Webtide.
Open Source Support
Mailing lists are a wonderful way to interact with the community at large and for a certain class of issue have the best chances of achieving resolution. There are a number of mailing lists available within the Jetty project. A good rule of thumb when choosing between the developer and user lists is to ask yourself who the audience is. If your question is broadly interesting to the community, use the users list, and if narrowly focused on Jetty internals or minutiae, then the dev list might be a better option.
Jetty Developers List
Jetty Users List
Jetty Announcements List
From a simple support perspective it is hard to beat StackOverflow for interacting with a Jetty community. Numerous users have asked and had answered their questions on the platform by other users and developers alike.
Github: Issues and Features
While not necessarily a support channel for solving a specific user problem, the issue tracker for Eclipse Jetty is a great location for addressing issues or suggesting features you want to see (or ideally contribute) in Jetty.
When you file a Github Issue in the Eclipse Jetty project there are a number of labels available and we encourage to you use them appropriately.
We have additionally identified and labeled a number of issues that may be appropriate for users of different levels of expertise that might want to contribute to Jetty but not have a specific goal or issue in mind.