I believe XP is calculated by the XP flowers that appear when you kill a unit. I could be wrong though.
Panzerfausts can be used against any targetable enemy building or vehicle, ambient buildings, I don't think so.
You can use it against fighting positions and cache's, but it is a pretty inefficient way of killing them.
Actually exp is calculated on the base of what kind of unit you attack(how expensive it is), how much vet it have and how much damage you did to it with an attack.
You can use pfaust against fighting positions or caches, but because they aren't really any expensive structures, you won't be getting much vet out of them.
The exp values from actual kills, vehicle or building destructions add up to your command point count.