What is the traction button next to the emergency brake and when would I use it?

You’d be better served by referencing the owner’s manual.

Your traction button is known as the Electronic Stability Control (ESC) button in your manual. The ESC system will be “On” whenever your Jeep is started or the power transfer unit (if equipped) is shifted out of 4WD LOW range. The “Partial Off” mode (pushing it so it illuminates) is intended for driving in deep snow, sand, or gravel. This mode raises the threshold for Traction Control System and ESC activation, which allows for more wheel spin than what ESC normally allows. You can turn it back on by pressing it and de-illuminating the button while the vehicle is in motion.