Drupal shows ?? instead of special characters with oracle
Check you are using UTF8 character set in Oracle database, and in apache config.
For data in Oracle db that is not UTF8 be careful if you need to convert, you need to identify what the original characterset is and the best way to convert to UTF8.


  The general rule of thumb is that if you are using UTF8 all the way
  you should not see those question marks in the browser.


Take a look here for Oracle UTF8 conversion info: https://stackoverflow.com/questions/8239250/how-to-configure-utf8-character-set-in-oracle