WooCommerce POS is a web application, therefore to print receipts you will need a printer capable of printing from the web browser. Thermal receipt printers seems to be stuck in 1980's technology, but some newer models do offer printing directly from the browser. For a suitably cheesy but somewhat helpful explanation check out this promotional video from Epson.
Below is a brief list of thermal receipt printers that should function with WooCommerce POS. Please note that we have not tested any of these printers, this list is only to provide a starting point for you own research, please read the reviews and do your own testing to make sure the printer will work as you expect.
Most receipt printers will include a RJ11 or RJ12 socket for triggering a cash draw. Each time a receipt is printed, the printer will trigger the cash draw to open. If you wish to use a receipt printer and cash drawer with WooCommerce POS you should check that the cash drawer has the right cable and your printer has the right socket.
The template for WooCommerce POS receipts can be customised by placing a new template file in your WordPress theme directory. The directory structure should be
/wp-content/themes/YOUR-THEME/woocommerce-pos/print/receipt.php. For more information on customising receipts please read the Receipt documentation.
If you have the stomach for it - and time - it is possible to put together your own internet connected thermal receipt printer. The process is definitely not easy but it actually looks like fun if you're a hacker/maker type. Read this blog for the initial research and then check this page for instructions and necessary equipment.