Khan Academy is not an educational institution.  I'm fairly sure I've seen posts by Khan Academy saying they don't give certificates or diplomas, and I don't think they give proof of attendance.

~ Janice (a Khan Academy user)

For one example, this response 3 years ago to someone asking for proof of enrollment:

... Khan Academy is not an accredited school; because of this, work done on the site does not count toward a degree program or diploma, and we cannot provide proof of enrollment for any coursework. Khan Academy is best used as a supplement to traditional schooling or homeschooling.  ...

Or this response 5 years ago to someone wanting their daughter's grades:

... while we provide learning resources that are aligned with many school needs, we are not a school, and there is no official enrollment for students online. We are not an accredited institution and do not provide teachers, transcripts, grades or enrollment records. ...

Harlow Rodriguez,

My comment with quotes from related threads and links to those threads has finally gotten approved; see above.