In the multitenant database, For getting an export dump from the pluggable database, It is a bit different process.

PLUGGABLE DATABASE(PDB) – PDBPRIM
SCHEMA_NAME – TESTUSER ( this schema/user is present in PDB PDBPRIM)

$ lsnrctl status

2. Add the entry in tnsnames.ora file for the pdb PDBPRIM.

3. Now create a directory for datapump under the PDB.(PDBPRIM)

SQL> show pdbs
SQL> alter session set container=PDBPRIM;
SQL> create directory PDB_EXPDIR as '/data/backup';

4. Now run the EXPDP:

$ expdp TESTUSER/TESTUSER@PDBPRIM dumpfile=TESTUSER.dmp logfile=TESTUSER.log directory=PDB_EXPDIR SCHEMAS=TESTUSER schemas=TESTUSER