So it looks like I can determine what custom form a field is used on, but I can't seem to figure out how to do "Where is a given custom form being used?"
In this example, I have a pre-existing task form, but due to it being created by another admin, not sure where it has been use, if it was ever used, or is it in current use. We think it may be a form no one has used in a while and would like to re-use the form and it's fields for a current use case. But we don't want to do that if it's in active use.
In one of the Adobe sessions they shared a report with the following text mode. Choose Report for your report type and add this text mode in the filter. It will show you any active custom forms that have not been attached to a project or template in the last year. You can modify the dates to your needs.
The approach I would take is to create a task report with the following EXISTS filter:
EXISTS:a:$$EXISTSMOD=EXISTS EXISTS:a:$$OBJCODE=TASK EXISTS:a:ID=FIELD:ID EXISTS:a:objectCategoriesMM:ID=YOUR CUSTOM FORM ID HERE EXISTS:a:objectCategoriesMM:ID_Mod=in
This will return all tasks in the system that has that custom form attached. Then a simple sort by entry date would give you an indication of when it was last used. You could also add the custom fields from this form to your report view to assess to what degree the form is being used.
Hope this helps.
In your task report, just select from the filters given. In the Categories section you should have one called ID. Just type in the name of your form and select it.