For privacy reasons a lot of data about a users viewership is not disclosed by Twitch.
If you want to track a user who is using an embed the only way to do so would be to have a login button on the site that has to be clicked before the embed is used, and then you could send data to your server when the user starts watching the embed (keep in mind this will also require a privacy policy, and everything else that’s required for legal compliance with privacy laws). This would only give you data on that 1 site that the embed is on though, you wouldn’t get data from embeds elsewhere.