You can't query directly to the work notes, and there also isn't a related list you can query to. 

It's also not very solid to have a report based on how many are created per time period, when the filtering is done on a field that can be changed anywhere during the lifetime of the ticket.

Next to that: work notes are string fields that are updated by users/integrations and a typo can cause it not to show.

If, for whatever reason, this really is an important thing to track, I would add a string or list field to the incident table (not on the form) and run a flow/br to update that field when a work note is added with the string you want tracked. Because with one word tracking, you will probably end up with people wanting to track other words as well. You can then create your report on <your_custom_field CONTAINS abc>.