Call the GET_GROUP_INSTALL_BASE and GET_SUBSCRIBER_BASE functions in the WWSEC_OID package in the PORTAL schema:
select portal.wwsec_oid.get_group_install_base from dual;
select 'cn=Users,' || portal.wwsec_oid.get_subscriber_base from dual;
Sample output:
GET_GROUP_INSTALL_BASE
------------------------------------------------------------
cn=portal.080916.233623.703000000,cn=groups,dc=disney,dc=com
'CN=USERS,'||PORTAL.WWSEC_OID.GET_SUBSCRIBER_BASE
-------------------------------------------------
cn=Users,dc=disney,dc=com