Plug a PDB in a new CDB without XML manifest
you can recover the XML file of a not unplugged PDB.


COPY the PDB folder into the CDB folder on the new machine.
Connect as SYSDBA to the new CDB (I use SQLDeveloper)
EXECUTE the package DBMS_PDB.RECOVER


it uses 3 parameters: 


/path/to/new/file.xml
NAME_OF_PDB (you can use the same as OLD PDB or a NEW ONE)
/path/to/pdb/folder/


EXAMPLE:

BEGIN
  DBMS_PDB.RECOVER (
  pdb_descr_file =&gt; '/path/to/new/file.xml.xml',
  pdb_name =&gt; 'NAME_OF_PDB',
  filenames =&gt; '/path/to/pdb/folder/'
  );
END;
/


THEN, you can plug the database using:

CREATE PLUGGABLE DATABASE NAME_OF_PDB USING '/path/to/new/file.xml' NOCOPY TEMPFILE REUSE;


THEN open the PDB:

ALTER PLUGGABLE DATABASE NAME_OF_PDB OPEN FORCE;


IF PDB DON'T OPEN, check PDB_VIOLATIONS

SELECT * FROM PDB_PLUG_IN_VIOLATIONS;


SOURCE
http://www.oraclebuffer.com/oracle/oracle-12c-lost-your-pdbs-xml-manifest-file-heres-how-you-can-recover-it/