To get this information, generate the Test coverage as you generally do. Open the generated test coverage report which by default shows for all the rules in the app. Use the field "Rules updated after" to filter out the rules and view the stats for a specified period starting from the date mentioned in the field to the current date (report generated date). It would show the list of rules covered and uncovered from the ones updated after that particular date.

You need to click on "Start new session" in test coverage landing page and then go and execute all your tests, come back and stop the test coverage session. You will be able to see the generated test coverage report.

You can generate this report at application level & user level (As you see 2 tabs). The metrics generated by application level report appear in application quality dashboard. Also, application level test coverage report can be generated across the sessions (multiple users can do testing between the start & stop of test coverage session) and a consolidated report would be generated. For user session, this is not possible as it applies to a single session.