VMS Help CMS, SHOW, GROUP, Command Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 group-expression

    Specifies the group to be listed. If you do not supply a
    group expression, CMS lists all groups in the library. A group
    expression can be a group name, a wildcard expression, or a list
    of these separated by commas.