how can I check on command line which plugins are activated?
For example I can enable/no-enable in foreman-installer, how can I see all which are enabled?
I use foreman with puppet, is there a “must” plugins which I have to enable it?
Not really command line but the current settings used by foreman-installer for the current scenario should be in the answers file in /etc/foreman-installer/scenarios.d, e.g. /etc/foreman-installer/scenarios.d/katello-answers.yaml if you have a katello server.