At the moment, we can only report or query based on the work type of a work item/request. 

In many cases, customers would want to know which form was used to raise a request. Though we can view it from the agent work item view, reporting and querying based on these details isn't supported yet. 

One use case I can think of: We configured two different customer experiences for support and partner, which will eventually create requests in the same space. For each Customer experience, I created a form for the same work type and space. 
These forms are added to the work item. I need to know how many partners/customers separately reached out about the particular issue. The ability to query based on forms used would help me achieve this. 

Partial workaround:

You can query which work items were created in which Customer experience via the following (undocumented) Entity Property and JQL:

issue.property["sd.channel.context.key"].channelIdentifier = "56705da0-c584-4ed3-ba6e-YOUR-ID"

You need to replace the value "56705da0-c584-4ed3-ba6e-YOUR-ID" with the actual ID of your customer experience.
You find this in the URL after navigating to the Customer Experience.