Can you tell if it is past the quick or not?
I just know that they can bleed a lot if they break off... which I'm assuming is why you don't know what to do with it. I can't tell you the best way to go, but if it does happen to break off and start bleeding, make sure you have some powdered ginger or turmeric on hand! Putting one of these on the spot that is bleeding can cause it to clot almost instantly.
If I were you, and it looks like it's broken past the quick, I probably wouldn't touch it- that might be vet territory. But, if it looks like it isn't past the quick, then probably go ahead and try.
Best of luck with your doggie!