Hello,

In the CSOM docs you can see a snippet for the selected rows:
http://help.infragistics.com/Help/NetAdvantage/NET/2008.3/CLR3.5/html/WebGrid_Object_CSOM.html

In the like manner you can iterate through the selected cells:

for(var cellId in grid.SelectedCells)
{
var cell=igtbl_getCellById(cellId);
alert(cell.getValue());
}

If you need the value from current cell (active cell) you can do it like
this:
grid.getActiveCell().getValue()