Unfortunately on ItemCommand the new order is not available yet. When the grid is sorted, the ItemCommand event is fired where the new sort expressions are added to the grid. Then the NeedDataSource event is fired and the sorted data is passed to the grid. After that on ItemDataBound the items are bound with the new order and you could retrieve it here. The new order of the grid items is available on PreRender event.
Find more information about the grid event sequence here
Please let us know if you need more help and if I missed something in my explanation.
the Telerik team