There's no secret to it - there is no per hub earnings. Some hubs are hits, and others are just NOT.
Hubpages doesn't provide a way for you or I to figure out how much any specific hub earns.
You could set up a Google analytics account and from there see how much you Hubpages account earns.
Most of us who spend a lot of time here - are also on several other websites that run adsense - and I personally just look to see what my adsense earnings are, and then I check my HP ad program earnings, and every once in a while, my amazon.com earnings.
My adsense earnings - could be coming entirely from other sites for all that I know. I don't care even. Hubpages is my favourite site for writing, reading, and trying to earn online - but it's hardly the only site that is similar. It's best to set up an adsense account and join other sites too. If you are trying to make a name for yourself, then you can't put every egg in the same basket.