When you have Shopbox open on the checkout screen, where you can see your products, press the printer icon, in the upper right corner.
Watch the image for further information:
Printer settings is now open. At the bottom of the pop-up window you can see the text "Shopbox ver. P 1.6.xxx.xxx" The 3 numbers that appear after "6." is the Shopbox version number, 414, which is seen in the image below.