The Reports To field is designed to map Manager field in Microsoft Active Directory and other LDAP servers. The Manager field is a distinguishedName (dn). Therefore it is in the format of "CN=FirstName LastName,CN=Users,DC=emarketdesign,DC=com".
If you don't have a Manager field set up in your Microsoft Active Directory or LDAP server, you can always create a custom field with this format and map it in the AD/LDAP Settings > Mapping tab in AD/LDAP extension.