In a CheckBoxClick event, here is code that displays the new value.
private void gridDataBoundGrid1_CheckBoxClick(object sender, Syncfusion.Windows.Forms.Grid.GridCellClickEventArgs e)
{
bool newValue;
object oldValue = this.grid[e.RowIndex, e.ColIndex].CellValue;
if(oldValue == DBNull.Value)
newValue = true;
else
newValue = !(bool)oldValue; //flip the true/false
Console.WriteLine(newValue);
}