I wish to add to the above.
The steps to Programming On the Main (POM) is slightly different depending on the manufacturer of your DCC system. I don't remember the button sequence on the Digitrax cabs to get to the POM stage. Your Digitrax user's manual will help with that. However, as Peteski mentioned, once you are there you can do the 'Query'. QSI's Query is simply CV 64 = whatever CV number you wish the decoder to speak.
The other feature Peteski mentioned is the 'Status Report'. By pressing F10, the decoder will speak it's status. While stopped, the decoder will speak it's address. It will also determine if it's in an advanced consist and report if it is. The manual also tells you how to use the Status Report to determine distance travelled, speed, a host of other features and which of these are verbally reported.
There is a caveat. Accuracy depends on doing the math. While the decoder will speak scale speed or distance, it's accuracy is determined by the circumference of the driving wheels and gear ratios. The manual also explains how to program these into the decoder.
There really is so much that these decoders can do. I find half the fun, after setting up appropriate momentum settings, is using the variable brake realistically. Learning is best done one step at a time. :-)