You can easily figure this out by downloading the current version of OST. The directory called "Upload" in the archive is what contains all the things that would have been saved/uploaded to your server.
dirs: api, image, include, scp, setup, styles.
base dir files: attachemnts.php, open.php, client.inc.php, offline.php, index.php, view.php, logout.php, captcha.php, secure.inc.php, login.php, tickets.php, main.inc.php.
You may not have a setup dir. (which is fine).
We cannot tell you where in your tree this directory resides of course since that would depend on who set it up in the first place, and whether or not it was integrated with another site in the same dir, etc.
