ost_ticket holds the tickets base information (ticket id, user that opened it, status, agent assigned to).
So if you know the ticket number you can look up who the assigned agent is.
SELECT staff_id FROM ost_ticket WHERE number=######;
Then you look up the Agents name and email in ost_staff.
SELECT firstname,lastname,email FROM ost_staff WHERE staff_id=#;
Or you can look up the user id and email id of the ticket owner.
SELECT user_id FROM ost_ticket WHERE number=######;
Then you can look up the user's name in ost_user
SELECT name FROM ost_user WHERE id=#'
And look up their Email in ost_user_email
SELECT address FROM ost_user WHERE id=#'