You don't find any table for the Jms Multi Sites extension as we don't save anything in the DB as we need to get the information before that joomla start and before any DB connection.
If you want to automatically redirect a user to a specific website, you have to imagine a rule somewhere that create the relationship between the user login and the slave site.
If you use the "owner" field that is associated to a slave site, you could perhaps retreive the list of slave site that is owned by a particular user.
The problem is what you are doing when you have several websites assigned to a given user?
So if you propose a service to create websites from the front-end, you can limit the number of website to 1 in the JMS Template rule (Maximum Website per user).
If you want to create a plugin and have access to some website information, see the chapter 4 of the user manual that descrbe some API to get info from a specific website.
If you want that we develop a specific plugin for you, this is something that we can do with our billable support that you can order at
www.jms2win.com/en/joomla-multisite?page...35&category_id=1