How to wire a 6-pin 1/4" audio jack?
Those are switched contacts. When the jack is unplugged R is connected to RN, T to TN, and S to SN.

You can use the contacts to bridge out a jack socket if nothing is plugged in. 
For example on a mic or guitar input I would connect RN to S so that the input is grounded and will be silent when the guitar lead is unplugged from the amp.