First, be sure that printing has been enabled for your event in the Event Manager.

Also, if you are using Photo Booth Upload, please note that when Auto Print is selected in the Printing Tab of PBU, the print option disappears in the Kiosk app, defaulting to the number of prints you've designated to auto print (or the Count Faces option).

NOTE: You can always print the last photo you've taken by clicking (or finger tapping on a touch screen monitor) the Upper Left Hand Corner of Photo Booth Upload.