If you mean to know sites that uses RSS News Feeds you may do that using the SQL queries below.
1. Get identification of module RssReader:
mysql> select id, code from module where code='RssReader';
+----+-----------+
| id | code |
+----+-----------+
| 10 | RssReader |
+----+-----------+
1 row in set (0.00 sec)
mysql>
2. Get aliases of all sites and their owners that use the module:
mysql> select distinct site.alias as site, user.user_name from site, user, module_instance where module_instance.site_id=site.id and module_instance.module_id=10 and site.user_id=user.id;
+-----------+-----------+
| site | user_name |
+-----------+-----------+
| test site | user |
+-----------+-----------+
1 row in set (0.00 sec)
mysql>