In English, without any indirect object such as "him/me," or "to him/to me," this suggests a very particular type of "show." If you "show a horse" or "show a dog" in English, it means you are exhibiting them at an official horse or dog competition. Unless you mean exhibit it AT A SHOW, you can't just "show" something in English without leaving your hearer hanging. The verb is begging for an indirect object, and it either wants to make "dog" the indirect object, in which case it wants a direct object, or it wants to find another indirect object: "Show the dog what? Or show the dog to whom?" If you want an intransitive verb that's akin to "show", you'll need to use a word like "exhibit" or "display" that stands alone.
Now, technically this sentence could work in conjunction with other sentences, or in the context of a conversation, like "He tells you to show Rose what you brought home yesterday from the animal shelter. You show (Rose) the dog," or "The dog doesn't know where its food is. You show the dog (where its food is)." But that's because the context gives you enough information that you can fill in the implied indirect object or direct object that is missing. Alone, it's completely ambiguous whether the dog is the direct or indirect object, and so English speakers will be confused about how "toont" is operating in this sentence. Which could get in the way of learning "toont," unless the same ambiguity exists in Dutch. The only choice that matches the amount of information given in English is "You show the dog (regularly, at competitions)."
I'd love to know which meaning in English is closest to what "Je toont de hond" means in Dutch. Do multiple answers work, or just one? A. You show the dog at dog shows. B. You exhibit the dog. C. You demonstrate something to the dog.
I completely understand what you mean! I ask this every time I come across this instance. My take on it though is that it probably doesn't need so much thought- above it was explained that your A & B instances would be correct but that the sentence doesn't translate as "to demonstrate something to the dog", as that would require a noun to fill in the blanks as to what that something is.
We're also early in our dutch studies, I say take this sentence at face value. Learn that all you need to know right now is what "toont" means, and I'm sure later as we learn more complicated lessons the more abstract meanings of various sentences will be filled out to us. You'll look back and wonder why you worried so much over this sentence, I'm sure!