Monomaniacs and their attendant bots keep trying to push the one-x spelling of to doxx, doxxing, doxxed (i.e., dox, doxing, doxed). You need only to look at the people promoting this to see that they are neither Americans nor native English speakers.
There is no traditional verb "to dox," as there is "to box." It is a recent neologism, and the favored spelling by and large is "doxx."
Thank you for your coöperation.