For decades, scientists have assumed canine heartworms spread globally alongside modern dog movement, but new genomic research co-authored by researchers from the Texas A&M College of Veterinary ... Possibly, "I do know that" can in fact only be used, when, you are answering the question of whether or not you know the issue at hand (or your knowledge has been called in to question, and you are answering that challenge). Let's say "out of the blue" you wanted to state that "you know that" -- and you wanted an emphatic version.

Understanding the Context