To view all server role membership requires

SELECT sys.server_role_members.role_principal_id, role.name AS RoleName,  
    sys.server_role_members.member_principal_id, member.name AS MemberName 
FROM sys.server_role_members 
JOIN sys.server_principals AS role 
    ON sys.server_role_members.role_principal_id = role.principal_id 
JOIN sys.server_principals AS member 
    ON sys.server_role_members.member_principal_id = member.principal_id;