Layers and structure in clean architecture

I currently woring on the topic clean architecture and trying to use it in my application. But I have recurring problems in the implementation.

The easiest way to explain it is an example:

I have: - an entity "user" in the domain layer - an use case "loginUser" in the application layer

But I have no idea how and where to provide the possibility to add a login listener.

I am also unsure about where to locate - the user repository? - the SQL implementation of the user repository?

Thank you