Hey wevrStephan,
MrGrr is right: you can easily cast to desired Blueprint and get a component or variable from its reference.
For more on Blueprint Communication, here’s some good documentation:
https://docs.unrealengine.com/latest/INT/Engine/Blueprints/UserGuide/BlueprintComms/index.html
You might also find this handy if you’re coming from Unity:
Hope that helps!