I feel like this thread is an incomplete unanswerable question.
Where is "Support ticket request created"?
Tickets are created when users click on the new ticket button/link which depending on if they are staff or clients take them to different places. Clients do indeed end up at: /open.php which is a form that clients fill out and create new tickets.
note: open.php also calls another half dozen or so php files. Including but not limited to /include/class.ticket.php and /include/client/open.inc.php
More importantly the string "Support ticket request created" is in the /open.php file on line 31.
So if this doesn't not answer your question I recommend that you frame your question with a little more information, and or ask it differently.