SQL> select TABLESPACE_NAME, ENCRYPTED from dba_tablespaces where ENCRYPTED='YES';

TABLESPACE_NAME                ENC
------------------------------ ---
MS_DATA                      YES
MS_INDX                      YES
TM_API_DATA                  YES
TM_API_INDX                  YES

SQL> select BYTES||'   '||FILE_NAME from dba_data_files where TABLESPACE_NAME in (select TABLESPACE_NAME from dba_tablespaces where ENCRYPTED='YES');

BYTES||''||FILE_NAME
----------------------------------------------------------------------------------------------------
1669595136   /mnt/CQ/data/ms_data_001.dbf
10485760   /mnt/CQ/indx/ms_indx_001.dbf
10485760   /mnt/CQ/data/tm_api_data_001.dbf
10485760   /mnt/CQ/indx/tm_api_indx_001.dbf

3 rows selected.