Check for Default Tablespace

Select username from dba_users
where (default_tablespace= 'SYSTEM' or temporary_tablespace= 'SYSTEM')
and username not in
('AURORA$JIS$UTILITY$', 'AURORA$ORB$UNAUTHENTICATED', 'DBSNMP',
'MDSYS', 'ORDPLUGINS', 'ORDSYS', 'OSE$HTTP$ADMIN', 'OUTLN', 'REPADMIN',
'SYS', 'SYSTEM','TRACESVR','MTSSYS','DIP');