can't you sum up total strain energy right from list selected?
this came up recently with our tech support group and we found a lot of great info in the SWX kb. you might want to check there on limitations
If you want the energy, use the other side of the equation. to the best of my knowledge SWX Sim does not report NL strain energy. For a linear analysis you can take the input force and multiply it by its displacement in the direction it is pointing and divide by 2. In an NL study it is the area under the load displacement curve for some node near the load application point in the component in the direction of the the load will get it close enough.