The information is stored in the wp_wc_comments_subscription table. You should store the users' information there. 

The red-marked wp_ is just a prefix. In your case, it can differ.

I'm curious about a piece of functionality. I looked through the docs, but didn't see anything related to what I am looking for. I am curious if there is a method, api call, etc. that I could use to manually subscribe a user to notifications for comments? I have a suite of custom plugins that I use, and it would be very helpful in my case to subscribe the authors of some content (they are NOT WordPress Author's due to a wide variety of reasons -- rather they are members of a custom role.) I am very comfortable in PHP development, and WordPress development in general.

Thanks!