The reader takes all its information from the xml-file, so unless it’s there it cannot be retrieved. 
If this is related to your other question I suggested a sketch for a workaround grabbing the efficiencies from the ROC curve there.
If you are interested in the total raw number of sig and bkg events you could read these from your input data, e.g. TTrees which can be done, although a bit inconveniently, at application time.
Cheers,
Kim