I can possibly think of a custom process which potentially can work (but haven't actually tried).
It is based on the theory that whenever any agent resolves a case with the KB, the resolution field is automatically populated with the KB links.
Whenever a record is saved with the Resolution Linke KB to Incident record is created/updated in Incident, fire a workflow which basically checks for the keywords to determine if the
Incident Resolution contains "Knowledge article link for Self Service clients: https://selfservice-"
Then do a field update to set a boolean field "Resolved with KB" = TRUE
Now in your reporting you can create filters/graphs on this field very easily.