I found the custom attribute icon_image which works perfekt with the icons from /usr/share/icingaweb2/public/img/icons.
I want to use some of my own icons and coby them to the directory, but there is no view on icingaweb2.
You should be able to place your own icons beneath /usr/share/icingaweb2/public somewhere. Though preferably a custom directory (path) as Web 2’s paths are managed by packages.
Then use the path relative to .../public (e.g. .../public/your/icon.png would be your/icon.png) and Web 2 should display the icons.