The C1GridExtender control supports sorting columns on the grid at run time. To allow users to sort the grid's columns at run time, simply set the AllowSorting to True. For example, with the following markup:

<cc1:C1GridExtender runat="server" ID="GridExtender1" TargetControlID="demo" AllowSorting="true">

To set a column's sort initial sort direction, set the SortDirection property on the column, for example:

<cc1:C1Field HeaderText="Number" DataType="Number" DataFormatString="n0" SortDirection="Ascending" />