Hi Thomas,
welcome back in our forum.
There is something like that with the community builder plugin cb_jemmyattending. But this is in the frontend cb user profile. If you have rights to enter backend, then normally you have the rights too to see the attendings of a user. This plugin works with the free actual community builder parts. But it doesn't show the new possibility of booking more places. Perhaps I hope will be a cb user which adds this possibility.
Also for you: The JEM community has no professional devs, we help each other too add new possibilities, to adapt JEM to the new Joomla versions and to make JEM better.
So please try yourself too to find a possibility to get your feature as much as you can and share it e.g. on
github.com/jemproject/JEM-Project
. There you are nearer to active devs. Hope to hear from you.
EDIT: Meanwhile I tried to add the number of booked places in the cb jemmyattending plugin and I gave it in github for control.