1* select distinct object_type from dba_objects order by 1
SQL> /

OBJECT_TYPE
---------------------------------------------------------
CLUSTER
CONSUMER GROUP
CONTEXT
DIRECTORY
EVALUATION CONTEXT
FUNCTION
INDEX
INDEX PARTITION
INDEXTYPE
JAVA CLASS
JAVA DATA
JAVA RESOURCE
JOB
JOB CLASS
LIBRARY
LOB
LOB PARTITION
MATERIALIZED VIEW
OPERATOR
PACKAGE
PACKAGE BODY
PROCEDURE
PROGRAM
QUEUE
RESOURCE PLAN
RULE
RULE SET
SCHEDULE
SEQUENCE
SYNONYM
TABLE
TABLE PARTITION
TRIGGER
TYPE
TYPE BODY
UNDEFINED
VIEW
WINDOW
WINDOW GROUP
XML SCHEMA

40 rows selected.

select dbms_metadata.get_ddl('TABLESPACE',tablespace_name) 
from dba_tablespaces
where contents='UNDO'
/

SQL> Declare
  2    line    varchar2(1000);
  3    nblog   pls_integer;
  4    i       pls_integer;
  5    j     pls_integer;
  6  Begin
  7    i := 0;
  8    dbms_output.put_line('  LOGFILE');
  9    Select count(*) into nblog from v$log;
 10    For cgroup in (select group#, members, bytes from v$log) loop
 11      i := i + 1;
 12      j := 0;
 13      line := '    GROUP ' || cgroup.group#;
 14      If cgroup.members > 1 then
 15        line := line || ' (';
 16        dbms_output.put_line (line);
 17        line := '';
 18      End if;
 19      For log in (select member from v$logfile where group#=cgroup.group#)
 20      loop
 21        j := j + 1;
 22        If cgroup.members > 1 then
 23          line := '      ';
 24        Else
 25          line := '';
 26        End if;
 27        line := line || '''' || log.member || '''';
 28        If j < cgroup.members then line := line || ','; end if;
 29        dbms_output.put_line (line);
 30      End loop;
 31      If cgroup.members > 1 then line := '      )';
 32      Else line := ''; end if;
 33      line := line || ' SIZE ';
 34      If mod (cgroup.bytes, 1024*1024) = 0 then
 35        line := line || to_char(cgroup.bytes/(1024*1024)) || 'M';
 36      Elsif mod (cgroup.bytes, 1024) = 0 then
 37        line := line || to_char(cgroup.bytes/1024) || 'K';
 38      Else
 39        line := line || to_char(cgroup.bytes);
 40      End if;
 41      If i < nblog then line := line || ','; end if;
 42      dbms_output.put_line (line);
 43    End loop;
 44  End;
 45  /
  LOGFILE
    GROUP 1 (
      'C:\ORACLE\BASES\MIKA\RL_G1_1.RDO',
      'C:\ORACLE\ARCHIVES\MIKA\RL_G1_2.RDO'
      ) SIZE 10M,
    GROUP 2 (
      'C:\ORACLE\BASES\MIKA\RL_G2_1.RDO',
      'C:\ORACLE\ARCHIVES\MIKA\RL_G2_2.RDO'
      ) SIZE 10M,
    GROUP 3 (
      'C:\ORACLE\BASES\MIKA\RL_G3_1.RDO',
      'C:\ORACLE\ARCHIVES\MIKA\RL_G3_2.RDO'
      ) SIZE 10M,
    GROUP 4 (
      'C:\ORACLE\BASES\MIKA\RL_G4_1.RDO',
      'C:\ORACLE\ARCHIVES\MIKA\RL_G4_2.RDO'
      ) SIZE 10M

PL/SQL procedure successfully completed.

SQL> with 
  2    data as (
  3      select g.group#, f.member, g.bytes,
  4             row_number () over (partition by g.group# order by null) rn_member,
  5             count(*) over (partition by g.group#) cnt_member
  6      from v$log g, v$logfile f
  7      where f.group# = g.group#
  8      order by g.group#
  9    )
 10  select decode(rn_member,
 11                1, 'alter database add logfile group '||group#||' (
 12     ',
 13                   '  ,') || 
 14         member ||
 15         decode(rn_member, 
 16                cnt_member, '
 17     ) size '||bytes||';',
 18                '') 
 19           ddl
 20  from data
 21  /
DDL
-----------------------------------------------------------------------------------
alter database add logfile group 1 (
   C:\ORACLE\BASES\MIKA\RL_G1_1.RDO
  ,C:\ORACLE\ARCHIVES\MIKA\RL_G1_2.RDO
   ) size 10485760;
alter database add logfile group 2 (
   C:\ORACLE\BASES\MIKA\RL_G2_1.RDO
  ,C:\ORACLE\ARCHIVES\MIKA\RL_G2_2.RDO
   ) size 10485760;
alter database add logfile group 3 (
   C:\ORACLE\BASES\MIKA\RL_G3_1.RDO
  ,C:\ORACLE\ARCHIVES\MIKA\RL_G3_2.RDO
   ) size 10485760;
alter database add logfile group 4 (
   C:\ORACLE\BASES\MIKA\RL_G4_1.RDO
  ,C:\ORACLE\ARCHIVES\MIKA\RL_G4_2.RDO
   ) size 10485760;

8 rows selected.

alter system set undo_tablespace = <new_undo_tablespace_name>;

The database must be in AUTO undo management mode (with the undo_management initialization parameter set to AUTO) 
in order for this parameter to be valid.

After the database comes up in auto undo management mode, Oracle Database selects the first available undo tablespace 
(or the one specified by the undo_tablespace parameter). Oracle Database dynamically adjusts the number of undo segments on and
offline in response to system activity. You can query the DBA_ROLLBACK_SEGS view to see the system-generated undo segments, as follows:

SQL> select owner, segment_name, tablespace_name from dba_rollback_segs;

OWNER  SEGMENT_NAME                   TABLESPACE_NAME
------ ------------------------------ ------------------------------
PUBLIC _SYSSMU15$                     UNDOTBS02
PUBLIC _SYSSMU16$                     UNDOTBS02
PUBLIC _SYSSMU17$                     UNDOTBS02
PUBLIC _SYSSMU18$                     UNDOTBS02
PUBLIC _SYSSMU19$                     UNDOTBS02
PUBLIC _SYSSMU20$                     UNDOTBS02
PUBLIC _SYSSMU21$                     UNDOTBS02
PUBLIC _SYSSMU22$                     UNDOTBS02
PUBLIC _SYSSMU23$                     UNDOTBS02
PUBLIC _SYSSMU24$                     UNDOTBS02
...

However, other than looking at the names, there's nothing you can do with these segments—Oracle Database manages them completely.
The V$UNDOSTATS view lets you look at all statistics associated with the UNDO tablespace, including the tuned_undoretention value over time, as in:

SQL>select tuned_undoretention from v$undostat;


TUNED_UNDORETENTION
-------------------
                900
               2700
               2700