C4D does not provide graphic representation of its shaders structure, neither
it allows to link one shader into several channels or materials.
Reference Shader attempts to cope with this flaw of C4D material system :
Reference Shader allows to reference one shader into any other shaders, even ones inside other materials.
Select a Shader window displays a list of materials and shaders helping to select the shader you want to connect to.
Unstested plugin - don't know if it works in recent versions of C4D or how it copes with reflectance