Translation:He always comments on things about which he knows nothing.
I wrote "He always comments about things that he knows nothing of."
"Of" had to be "about". "He knows nothing of me." is a good sentence. Why can't it be used in this sentence?
I had a similar problem. "Of which he knows nothing" was dinged at the "of."
I reported it.
And I also found myself thinking about BookFace.