That's a good question. The only way I can think of to track which hubs are earning HP Ad Program money is to do it through Google Analytics. It won't be an exact correlation between your hubs and HP Ad Program income, but it will tell you which hubs are getting the most traffic and therefore views/impressions, which, as melbel stated, is how the HP Ad Program pays. From that you can extrapolate which hubs are your top HP Ad Program income earners. Hope that made sense. I'd be interested in seeing how other hubbers answer this.