Per point data (vertex maps) defined by an object can be accessed via the Cinema 4D Vertex Map shader. You must add a Vertex Map shader to the network and drag & drop the selected Vertex Map from the object to the Vertex Map parameter.
Vertex maps are exported as user parameters with a vmap_ prefix and lower case. For example, the vertex map named My Vertex Map is exported to vmap_my_vertex_map. You can also use the user_data shaders to read these values.
By default, all vertex maps of an object are exported to Arnold. To specify only a subset of the vertex maps or completely disable vertex map export, you have to add an Arnold tag to the object and change settings on the Export tab.
Vertex map connected to the Base Weight of a standard_surface shader
Multiple vertex maps connected using the 'mix' shader