The serial number on the iP110 is located on the back of the unit, just to the right of the battery connector.  In this image, the cover for the battery connector has been removed.

The serial number has four letters and five numbers.

The serial number is also the default password used by the printer when it is configured to be used in Access Point mode (this allows wireless computers and mobile devices to communicate with the printer without a wireless router).  You can print the Network Configuration Page from the printer to see the password.

Please note that AZDK is part of the FCC information and is not the serial number for your printer.