Fake
https://hoax-alert.leadstories.com/3470852-fake-news-mark-twain-no-amount-of-evidence-will-ever-persuade-an-idiot.html
In religion and politics people's beliefs and convictions are in almost every case gotten at second-hand, and without examination, from authorities who have not themselves examined the questions at issue but have taken them at second-hand from other non-examiners, whose opinions about them were not worth a brass farthing.
- Autobiographical dictation, 10 July 1908. Published in Autobiography of Mark Twain, Volume 3 (University of California Press, 2015)
An Australian fact checker also researched the quote and declared it fake:
The Mark Twain House & Museum in Hartford, Connecticut was the author's home from 1874 to 1891 and among its educational aims today is to assist in the teaching of Twain's "life and works".
A museum spokeswoman told AAP FactCheck that its curatorial staff found "no trace" online which supported attribution of the quote to Twain "other than in the usual inspirational or business works".
Since -- as Mark Twain never said -- no amount of evidence will ever persuade an idiot, we will stop here.
