Probably as high a percentage as his supporters. Trying to deflect criticism by saying people hadn’t read it was a common way to avoid critically thinking about it, and it became comical when people were making very specific comments which clearly indicated familiarity. I remember someone writing a very detailed critique of the way it was oversold it as based on science despite misrepresenting the scientific consensus[1], and even then you could easily find people saying that the reason she didn’t agree with him was that she hadn’t read it or that buzzfeed published the text first without charts, even when she was discussing the original studies he was claiming as support.

1. https://medium.com/@tweetingmouse/the-truth-has-got-its-boot...