The button is directly in-line with the LED and signal. So if the light is operating correctly, the button is working.
Pinout and Schematic
In the image below, is the key for the wired connection between the touch sensor and the robot controller. The touch sensor does not use or pick up a signal from the n (blue) wire. This is not a problem if there is one digital sensor per port. However, If you intend to connect more than one digital sensor to the same port using the sensor splitter cable, make sure that the n+1 (white) wire portion of the splitter cable is plugged into the touch sensor.