Which path should you take?

You are walking your dog on a foggy day. In this city there are knaves, who always lie, and knights, who always tell the truth. Suddenly your dog barks and runs off without you noticing it. The next thing you know is that you are chasing after him and you are now standing in a clearing with three paths. You know that only one of the paths lead to your dog and the others lead to a bottomless pit. You then see a stranger standing by but you don't know if he is a knight or a knave. How many questions (at least) do you need to ask him to find the right way?

Note: The stranger knows exactly which way your dog took.