AMQP 0-10 requires to use a unique session name. If session with a given name already exists, the attach attempt ends up in detach being sent from broker with session-busy detach code. The attach session name is not exposed in any way via management. Thus, it is not possible to determine what session names are already used.
Potentially, the name provided in attach can be exposed as a derived attribute. It will allow to debug and identify such issues like client disconnects due to session name being already used by other sessions.