Look in the passport (on the page with the passport number on it.) You will see a Issuance agency/Place. It may just say Passport Agency.. It may be an actual city if you got it in one of the cities that has a passport office.
It can be confusing since they ask for a city when it really doesn't have to be a city.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007