I have a Root Node that Contains a C# Script, now i want to reference the TeileBibliothek GDScript of its immediate Child, to read the data from it... is there a way to do it or am i screwed?
Cross-language Scripting
...and also check out the docs, which have examples in both directions: https://docs.godotengine.org/en/stable/tutorials/scripting/cross_language_scripting.html
I'll assume this is the bit you're mostly interested in: https://docs.godotengine.org/en/stable/tutorials/scripting/cross_language_scripting.html#calling-gdscript-methods-from-c (which works, not only for methods, but setter/getter(s) too)