Contact
You can contact contact@grapheneos.org for topics related to GrapheneOS. The security@grapheneos.org address can be used for high priority security issues. The email address of the lead developer is danielmicay@gmail.com as a fallback option for anything else.
The official Twitter account for the project is @GrapheneOS which is used for official announcements. The account of the lead developer is @DanielMicay and is primarily focused on the privacy and security research/engineering work on GrapheneOS.
Community
The main forum currently used to discuss the project is the official /r/GrapheneOS subreddit on Reddit.
The main IRC channel is #grapheneos on irc.freenode.net. The channel is bridged to Matrix and is available at #grapheneos:matrix.org for Matrix users.