By default, a non-admin user won't know that another non-admin user exists in a workspace with them, even when both users are part of the same permission group. Non-admin users also do not know the name of the Custom Group they belong to. Only administrators can view the existing members of a workspace and can access all of the information found in the Permissions page.
All questions submitted and responses received in the Q&A Version 1 module are only viewable between a single user and administrators.
Notice for EZ Q&A (Version 2)
If EZ Q&A (Version 2) is enabled for a workspace and the "Show the names of users on Q&A activity" feature is also enabled for a question group, the non-admin users of that group will be able to see the names of their fellow non-admins within that group for questions and replies. They will only be able to see the names of the members of that group and admins, but can't see the names of members within a different question group.
You can enable or disable EZ Q&A (Version 2) from the workspace Settings page > check or un-check the box next to "Use the EZ Q&A feature on this workspace." > Save Workspace Settings.