how do you know if infant has ear infection - Viral Trends
Since toddlers often can’t verbally tell you their symptoms, it's important to know the visual cues they may have an ear infection. Possible duplicate of "Know about" vs. "know of".
Understanding the Context
Also What are the differences between “know”, “know about”, and “know of”? on English Language Learners, which is probably a better site for questions like this. 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.