@LNSiefert
While it isn't a part of the Canvas UI yet, there are some API calls that will allow you to see if there are any Rubric Associations.
I currently have a free Chrome extension (Canvas LMS Mods) that you could use if you aren't comfortable with using the API. My extension doesn't use the new endpoint yet so it doesn't provide the specific details about the assignment name nor the course the assignment is in; however, it does let you know if it is associated with any assignments and the ID of the assignment. I will need to look into updating this now that I see the new endpoint.
With the Chrome extension installed, on the Rubrics page there is a "Load Rubric Details" button that is added below the "Add Rubric" button. This will add in information like whether or not it is associated with any assignments. You can also go to an individual rubric and below the rubric there is a Rubric Association report you can run. This will show the basic information about the Rubric Associations for the rubric: the type of association (Assignment, Course, or Account), the ID of the associated item, whether or not it is used for grading, and its purpose.
You can learn more about the background and list of features of the Chrome extension I developed here: Creating a Chrome Extension to Use with Canvas LMS