I've owned a number of dogs over the years. I think one thing you can say about dogs in general is, they're pretty much just thinking about their own needs. On Maslow's hierarchy of needs, not many dogs make it past level two-okay, to be fair, maybe level three. Dogs do tend toward the affectionate. All in all, dogs are really pretty selfish. There isn't anything wrong with that. It is what it is. Dogs live on their instincts, pure and simple. What is there to eat? Scratch that spot-right there. Can we go outside? These are the worries that most concern dogs. I love dogs-more than any other kind of animals. But, I don't think you're going to see a whole bunch of forward thinking in dogs. They live in the here and now-concerned only with their most immediate needs.
I won't say that dogs go through the day completely without thinking. I'm just saying that all their thinking is instinctual. One of my dog's favorite hobbies is to stare out the window. The sill is at the perfect height where she can just rest her head and look out at the world enjoying the sights and, more importantly, the smells. Now, when she's sitting there, I'm not saying she's completely without thought. I'm just saying she isn't thinking about anything other than what's in her immediate environment. And, like a child with ADHD, her thoughts are easily distracted. What's that smell? Oh, look, a bird. Hey, is that a dog in my yard? Woof!
What dogs won't think about are future events. Let's see, I have a vet's appointment a week from Thursday. They aren't even thinking in the immediate future. After five more minutes of staring, I'm going to get some more kibble. No, dogs react to what they see in front of them and that's it. Again, there's nothing wrong with that.
Now, I realize, there are exceptions. If you catch a dog early enough, (s)he can be trained to do a number of things. Seeing eye and other service dogs come to mind. These animals are trained to learn specific tasks in specific situations. You could say they are thinking, but even then, it is the immediate environment that is most important. They keep their humans safe, because it's how they were trained. They don't know anything different.
So, what is your dog thinking about? Good question. In my experience, the average dog is thinking about him or her self. And, as much as I love dogs, I really don't have a problem with that.