The example can be found in the RestFrames package at
examples/example_Wlnu.C
You can run the compiled example executable:
./examples/example_Wlnu.x
or run the example from the ROOT interactive command line:
root [0] .x examples/example_Wlnu.C+ //ROOT5
root [0] .x examples/example_Wlnu.C //ROOT6
For the latter, if RestFrames is not installed in an area in the
default PATH then you must first load the RestFrames
environmental variables with source setup_RestFrames.(c)sh. You can
find additional details about running RestFrames examples here.