What the dog is saying it's some kind of pun, instead of saying こんにちは (konnichiwa=hello) it says こんにちワン (konnichiwan). "Wan" is the japanese equivalent for "woof", so it could be translated as "konnichiwoof" or "hellowoof".
Ah, I've encountered a pun like this myself in the past...even though in Japanese he is not asking a question, a localization attempt might be something like "Bow-Wow are you?" like "how are you?". I realize that he is not asking a question, but on the other hand, "how are you" usually occurs after one says "hello". Its not the best idea in the world, but its just my two cents.
