[Simple] get jqGrid cell data with index of columns

var colModel = new Array();
    colModel[0] = { name: "id", index: "id", width: 10, sortable: true,... };
    colModel[1] = { name: "name", index: "name", width: 50, sortable: true,... };
    colModel[2] = { name: "detail", index: "detail", width: 100, sortable: false,... };
     .....

$("#GridID").jqGrid({
                colModel: colModel,
                ...
});

function GetCellDataByIndex(index){
     var g = $("#GridID");
     var id = g.getGridParam("selrow");     //g.jqGrid('getGridParam', 'selrow');
     var rowData = g.getRowData(id);        //g.jqGrid('getRowData', id);
     var cellindexdata = rowData[colModel[index].name];
}

// It very easy to understand.