You buy it from one of the vendors that tracks people... There are literally businesses out there that gives you a snippet to embed in your site, and then they

You buy it from one of the vendors that tracks people... There are literally businesses out there that gives you a snippet to embed in your site, and then they employ all the tricks of tracking to give you email, name, address, etc. It's not perfect every time, but probably more that you would like. And I wouldn't be surprised if incognito mode or VPN isn't always enough to disappear.