Why do you think that He doesn't know him from his schooldays means that he does know him? It would only have that sense if you added something like In fact, he first met him at university. 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).

Understanding the Context

Let's say "out of the blue" you wanted to state that "you know that" -- and you wanted an emphatic version. "doesn't know" vs "don't know" [duplicate] - English Language & Usage ... MSN: Realty TV Fans Want to Know Who Leaked the Taylor Frankie Paul Video Fans of The Secret Lives of Mormon Wives star Taylor Frankie Paul want to know who leaked the video that shows her involved in a heated domestic incident with her ex-boyfriend, Dakota Mortensen. Realty TV Fans Want to Know Who Leaked the Taylor Frankie Paul Video Waterloo Media Conservative Talk 590/99.7 KLBJ dips 5.4 to 5.1.

Key Insights

iHeartMedia Country 100.7 KASE holds at a 4.1 share. Christian AC “ K-Love ” 105.9 KFMK subscribes for the first time showing a 3.1 to 4.1 gain. Beasley Media Classic Hits 105.7 WROR rises 6.9 – 8.4 – 9.2 to lead Boston. Ratings Expert Chris Huff notes that is the largest share ever in the history the station. Beasley’s “ 98.5 The Sports Hub ” WBZ-FM rises 6.3 to 7.3 to move up to second just ahead of Audacy AC “ Magic 106.7 ” WMJX as it rises 6.7 to 7.2.

Final Thoughts

iHeartMedia Classic Rock 100.7 WZLX is fourth up 5.2 to 5.9, while ...