You can contact firstname.lastname@example.org for topics related to GrapheneOS. The email@example.com address can be used for high priority security issues. The email address of the lead developer is firstname.lastname@example.org 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.
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 #grapheneos channel on irc.oftc.net is an alternate channel acting as a backup for when freenode is down.