I signed up for TSA Pre Check but I don't know my number. How can I get the number? How do I know when it expires?
According to the TSA Precheck FAQ:
I forgot my KTN. How do I find it?
If you are a member of the TSA Pre✓® Application Program, look up your KTN online.
If you are a member of another trusted traveler program, such as Global Entry, NEXUS, or SENTRI, log on to the Global Online Enrollment System or GOES account to obtain your PASSID, which is your KTN.
You should just be able to follow the link, enter your personal information, and get your KTN (known traveler number). That's the number you'll provide when you make air reservations to use Precheck.