Does your dongle hang low? Does it wobble to and fro?
Obviously this guy doesn't have a real copy, come on now. Even if that's the case, a search in Google with a very broad query came up with the answer in the first result.
The monitor button is the little button the mixer that is right above the red recording button. When you click it, it should turn yellow, and be activated.
Pretty sure the Tascam us-428 comes with cubase lite which doesn't require a dongle.
midwest, try doubleclicking the little speaker in the lower right corner of your screen and then choose options/properties. Make sure the correct box you need to monitor your tascam is checked.