コーパス検索（https://corpus.byu.edu/now/）してみた感じだとそれなりの数の
まったく同じ形の文章が引っかかります
("_v* who knows how many _nn*")
He could have killed who knows how many people, because at that time there were 10 people working on setting
I had passed who knows how many times, walked by without much of a second thought.
You know we've built who knows how many schools.
>>136に同意でこの英文をそう読めないなら英文を読んだ量が足りない
ある程度の英語力があるようだしもっと色々読んだら良いと思いますよ
