please provide more information:
how did you implement data masking ?
I guess you have to revoke the privileges required for running the masking process, for example:
SELECT ANY DICTIONARY
EXECUTE on SYS.DBMS_CRYPTO
remove the DM_FMTLIB package
With all this revoked from the users granted to masking should be enought in 11g
Why do you want to disable it? Just don't use it.
If the question is really "How do I see the actual data that has been masked?" then you need to have DBA role or login as sysdba, if you have masked the data using dbms_crypto.
...and when you refer to an Oracle "doc", please include the link to that doc or article so we can see what you are referring to.