We currently don't support a shadow effect on pie or donut charts.
However, we do have a range of effects you can apply to your donut or pie chart by using the "chartEffect" property on your series' style object.
Here is an example of setting one of these effects:
SChartPieSeries *series = [[SChartPieSeries new] autorelease];
series.style.chartEffect = SChartRadialChartEffectRounded;
Let me know if you have any questions.