Trump’s reference to email is based off a report in The New York Post. The gist of the Post report is that Biden used his position as vice president to enrich his son Hunter – an unsubstantiated argument peddled by Rudy Giuliani and other Trump supporters.
The New York Times, Washington Post and Wall Street Journal have reported that they could not independently verify the information in the Post article.
Our colleague Adam Goldman did a long dive into the New York Post report. It’s worth a read: