Hi, Max.
Socialize is a Joomla! template - not a JomSocial template (layout) :)
It's like Protostar or any other Joomla! template and you'll find it here: Backend -> Extensions -> Templates
Yes, you may set it only for JomSocial pages only if you want.
If you log in the site ( music.kanoon.de ) and navigate to an event you'll see that the header is gone...
HI, Max.
Did you customized any of template files?
Could you provide FTP access to dev site? Current FTP are rather for your production site.
HI, Max.
Fixed.
Please, check if this work for you as well.