Thanks for using Aspose APIs.
Please use the Shape.GetResultOfSmartArt() method to convert your shape into group shape. Please use the Shape.IsSmartArt property to determine if shape is a smart art shape.
Please see the following sample code and its console output for your help.
//Load source Excel file
Workbook wb = new Workbook("Demo-Shapes.xlsx");
//Access first worksheet
Worksheet ws = wb.Worksheets;
//Access this Smart Art Shape
Shape smShape = ws.Shapes["Diagram 4"];
//Check if this shape is smart art shape
if (smShape.IsSmartArt == true)
//Convert it to group shape and access all indvidual shapes
Shape shapes = smShape.GetResultOfSmartArt().GetGroupedShapes();
foreach (Shape s in shapes)