public class CIMVoxelStretchRenderer : CIMVoxelRenderer, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

//var voxelLayer = ... ;
//Must be on the QueuedTask.Run()

var variable = voxelLayer.GetVariableProfiles().First();
var renderer = variable.Renderer;
if (variable.DataType == VoxelVariableDataType.Continuous)
{
    //Renderer will be stretch
    var stretchRenderer = renderer as CIMVoxelStretchRenderer;
    //access the renderer

}
else //VoxelVariableDataType.Discrete
{
    //Renderer will be unique value
    var uvr = renderer as CIMVoxelUniqueValueRenderer;
    //access the renderer
}