How to keep events and their listeners organized?

Asking for a friend, obviously...

Say, you a have a well kept legacy codebase with a nice framework in place. It's a rather big piece of monolithic glory. It's maintainable. We're well off.

But the concept of triggers, events and listeners gains traction and now events and listeners are popping up left and right. (When all you have is a hammer...)

Now, nobody is demonizing the concept of events and I... err, my friend has used events and listeners quite successfully. But this feeling of being flooded is setting in. You know, when you are not sure if you have seen that exact event message once or twice before. Are we having multiple messages for the same event in different places? Am I listening to the right event?

So I was wondering if you guys have a strategy or style of documentation that would help keep things, at least apparently, organized.