How do I know if my dogs has a broken toe?

Ouch! Well, the easiest way to find out if it's broken is to get it x-rayed. Dogs have individual pain tolerances, and a soft-tissue injury can hurt more than a simple fracture. I've seen dogs practically waltz in, and have a fracture, and I've seen dogs refuse to even place the foot down at all, and refuse to let anyone touch the foot, and not have any broken bones. Depending on how uncomfortable he is, you have the option of waiting to see if he gets better on his own, but I recommend radiographs.

The Toe will be swollen. Your dog will probably limp or not want to put much pressure on the paw. The dog may also not want you to touch the paw. He may lick at the area.

Similar to what Shannon said, it's best to monitor their behavior. If your pup is still sensitive, limping, or shows aggression when trying to touch its paw the next day, it's best to go to the vet and check it out. They'll be able to x-ray it, and provide any pain meds or antibiotics that will make your pup happy and comfortable.

If you are really worried and your pup is still walking funny I'd take it in to be x-rayed at the vet!

I would take the dog to the vet to be evaluated. Hope he feels better soon!