I'm searching for the opportunity to use the existing wiki in Redmine project independent.
Why project independent?
I need it for general topics and plugins which are not part from a project.
Or exists a plugin which I can use for this?
People generally create a "General" project or something similar for the global stuff.
Everything in Redmine is part of a project. There are no global areas with user-acccessible data. This is by design, is leveraged by the permissions system and other areas and is not about to change.