Which animal would you like to have as a pet? Why?
Maybe A dog
Because dogs are awesome :)
As a pet, I would like to have maybe (the) a dog, I do not know why :) -> GOOD! KEEP GOING!
maybe the dog I do not know why :) The other corrections are good.
I might say:
A dog would be a good pet. I like them, I don't know why.
Maybe a dog. I do not know why :)