There is no such thing in ASP.NET Core. sitemaps don't really play well into how MVC works. Furthermore, unless your site is dynamically generating routes from the DB as well like a content management site, then sitemaps stored in the DB don't really make any sense at all. Just because there is some URL in a database doesn't mean it actually exists. To get the actual information you would really need to just look at the routing table that the runtime uses. But you'd need to annotate it so you could tell the difference between routes you want in the map and those you don't.
Here is a link to one person's attempt at getting sitemaps working in ASP.NET Core. You can check out their solution and see if it might fit into what you are looking for.