Hi,
this feature was removed, because of security reasons: Maintenance: Improve session takeover handling. · zammad/zammad@8103fc5 · GitHub
It was also never really used in the code base. The question would be, what problem do you want so solve?
Maybe some existing events can be used, but currently, there is no idea of the possibility of custom events.
Also with the technical rewrite and the usage of the action cable the complete old web socket server will be dropped at some point.