I look for a string on the page, and then search the files for the string.
So if the string (text) on the page says "Open a new Ticket", then i would search for that in all files in the project.
You can also look in:
/include/client for User UI
and
/include/staff for Agent UI
If you cant find something even with search then you can ask and someone here might be able to point you in the right direction.