public enum VoxelVariableDataType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

//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
}

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

//Get the variable profile on which to access the data
var variable = voxelLayer.SelectedVariableProfile;
//or use ...voxelLayer.GetVariableProfiles()

//Data range
//At 2.x - 
//var min = variable.GetVariableStatistics().MinimumValue;
//var max = variable.GetVariableStatistics().MaximumValue;

var min = variable.Statistics.MinimumValue;
var max = variable.Statistics.MaximumValue;

//Color range (Continuous only)
double color_min, color_max;
if (variable.DataType == VoxelVariableDataType.Continuous)
{
    var renderer = variable.Renderer as CIMVoxelStretchRenderer;
    color_min = renderer.ColorRangeMin;
    color_max = renderer.ColorRangeMax;
}