Not sure how much more detailed I can get wihtou you really explaining what you are trying to do?
The Firmata libraries use a callback, not an interrupt. This sort of works like an interrupt in that your software function is just invoked when needed, but you should look at the example code to work it out. My point is that if you want to have a visual confirmation that the routine has been called, you should change something you can see outside of the program that is running. A LED is an obvious choice. An alternative is to increment a number that you can display outside of the callback (ie, in a global variable).