Hi there,
Jetpack comments is just a skin that’s added to the built-in comments feature in WordPress, so the comments are still stored in the wp_comments
table in the database. And then it syncs comments to the cached copy of your site on WordPress.com so you can manage comments using WordPress.com’s tools.
The only change Jetpack essentially makes to comments is that people who visit your site while logged into a WordPress.com account are automatically logged in for commenting, i.e. they don’t need to manually type in their email address on the comment form, and it also allows people to log in via a social media account if you allow that option. It doesn’t make any changes to how comments work in the background.