How can I check to make sure my Dell XT2/HP tx2/Lenovo T410s MT device is working?

You need to make sure you know your input device, first. See above.

First, evtest the dev node. For example, if you've got an MT device at /dev/input/event5, then do the following:

  sudo evtest /dev/input/event5

You should see lots of data printed when interacting with the device.

If, however, you see no data or evtest doesn't support your MT device, you can use lsusb against the usbmon functionality of the debug filesystem instead:

  sudo cat /sys/kernel/debug/usb/usbmon/ \
   `lsusb | \
    grep -i N-Trig | \
    cut -f 2 -d ' ' | \
    sed 's/^0\+//' | sed 's/$/u/'`

What this basically does is tells you (hopefully) that the device is connected and recognized at the raw USB device level. usbmon show you the traffic between the device and the kernel.