public class VoxelVolume 

{
  // Note: call within QueuedTask.Run()
  {
    //Use the SelectedVariableProfile to get the slices currently in the TOC
    //via its associated volume
    var volume = voxelLayer.SelectedVariableProfile.Volume;
    var slices = volume.GetSlices();

    //Do something... e.g. make them visible
    foreach (var slice in slices)
    {
      slice.IsVisible = true;
      volume.UpdateSlice(slice);
    }

    //expand the slice container and make sure container visibility is true
    voxelLayer.SetSliceContainerExpanded(true);
    voxelLayer.SetSliceContainerVisibility(true);
  }
}

{
  //Use the SelectedVariableProfile to get the slices currently in the TOC
  //via its associated volume
  var volume = voxelLayer.SelectedVariableProfile.Volume;
  var slice = volume.GetSlices().FirstOrDefault();
  var slice2 = volume.GetSlices().First(s => s.Id == my_slice_id);
}