There are a couple options. If you don't use a receipt printer currently you can get a USB printer that Works with your Square stand. If you already have one you can just turn on orders to print to it.
As far as a Wifi printer all the printers require ethernet to connect. You could turn on the iPad hotspot and get an Apple airport express, This will connect wirelessly to the iPad and provides an ethernet port for the printer. While I have not used this configuration for this situation it should work.
