To print a list from the mobile app, swipe left on the list name and tap the ... button to access list settings. Tap "Print". This will open the list as a PDF on your device.
From the web or desktop app, open the list and click on it's name to access list settings. From there, click on "Print" in the "Actions" section of the settings. If using the desktop app, this will create a PDF you can print. In the web app it will open your browser's print window.