The release number and name are stored in the VERSION file of your DokuWiki Installation.
You can check the version of your installation by logging in as a superuser and use the do=check parameter to your wiki's URL. Eg:
http://yourdomain/yourwiki/doku.php?do=check
Please note that for security reasons, the check command will not display version information unless you're logged in as superuser.
Another method of checking your dokuwiki version is to go to the admin page, where in the content area under the menu on the right hand side, the version number with its code name will be displayed.