Find direct connections to database server instead of SQL Server Always On Listener
I covered this through two main posts. The first gives you an idea how to see what is being used, currently. The second tells you how to find which connections are read only routed by exploiting the fact that SQL Server can listen on multiple ports and that read only routing accepts whatever endpoint url you give it which is directly given back to the client - this means you can setup specific items just for read only routing and report back on it.

It is much more accurate and no need to go through extended events. You're specifically looking for the second post, but they are related and will give you a better picture when combined together.


Finding What Availability Group Listeners Applications Are Using To Connect
Finding Which Connections Have Been Read Only Routed