Who teaches “Knee on back of neck” in Bjj?

This brown belt does!

https://www.nbcnews.com/news/us-news/wrestling-coach-washington-state-fired-over-post-george-floyd-s-n1217881

Nobody had to master “Knee on neck” to get a blue belt? 

You can see that technique near the end of this Karate ad.

https://youtu.be/n7PEMGuA6tw