I can't find a picture of it, but I did find an explanation. It's going to be a five digit number. The first two numbers will be a year, so probably a 13 or a 14. The next three digits represents a day within that year, so they'll be a number between 001 and 365, I'd think.
Most expiration dates are on the flaps of the box, so I'd look in those areas. It might have an EX in front of the five numbers, like EX 13145.
You should be able to find the expiry date on the Digiorno Traditional Crust Four Cheese pizza on the front flap or the side flap of the packaging box. If you can't find it, it would be a good idea to contact someone from the DiGiorno help desk.