How do I use shatter effect on one specific thing?

1. Duplicate the footage layer twice
2. Name the top copy "shatter"
3. Name the middle copy "fill"
4. Cut out the one thing in the layer you want to shatter using an animated mask of some type
5. Pre-compose the shatter layer to get a nested shatter comp
6. Add shatter to the nested shatter comp
7. Animate the force or use a custom shatter map or any of a dozen other techniques to get the top layer to shatter
8. Now comes the hard part: go to the fill layer and use whatever tools you need to use to fill the spot you have cut out in the shatter comp layer so when the top layer shatters the original object does not reappear.

This is easiest if you locked off the camera and shot a clean plate with nothing in the shot where the person (object) you want to shatter is standing or walking or whatever they are doing. If you do not have a clean plate expect to spend hours trying to fill behind your actor. Without the proper planning, this can be nearly impossible. If the camera is moving the difficulty factor just went up by about 100.

To give you specific instructions we would have to see the shot you are working on.