Do dogs know when they are being praised?

Without a wagging tail, the dog will rely solely on the tone of your voice.

I have never trained dogs using treats.  I only use praise - and that includes when I was housebreaking them.

Yes, MY dogs know.

Yes but only by the sound of your voice.

Body language and tone. I can make my voice all cute, high, and stupid, go up to my pup like I'm going to rub his tummy, all while calling him a stupid piece of crap, he sucks, he smells like poo, but as long as I'm going in for pets and talking this way, he doesn't care. If I was to make myself bigger and shout that I love him and he's the best, goodest dog in the whole world while yelling angrily, he would be terrified. 

My friend is a dog trainer who deals with people who swear up and down, "My dog knows English. My dog uNdErStAnDs mE." Her favorite thing to do is to make them sit, but instead of saying 'sit' she says 'potato' in the same tone they would use. And it works. They sit. They will learn SOME words here and there along the way, but it's mostly all about HOW you say it and how you approach them.

Dogs respond to body language and tone of voice more than anything else.

They do learn a few words when used consistently.

You could tell your dog it was a horrible animal and issue dire threats but if you did it while smiling and in a happy sounding voice your dog would interpret it as praise.

Their tails would seem to indicate they do.