Telerik getting selected ID (Get data from Radgrid selected item)

This is what data keys are for. Just designate the columns you want to access as data keys, like in the example shown below.

<telerik:RadGrid ID="RadGrid1" runat="server" ...>
    <MasterTableView DataKeyNames="Column1, Column2, Column3" ...>
        ...
    </MasterTableView>
</telerik>

Once the data keys have been assigned in the markup, you can access them in code-behind by row, or using the SelectedValues property.

if (RadGrid1.SelectedItems.Count > 0)
{
    //access a string value
    string column1 = RadGrid1.SelectedValues["Column1"].ToString();

    //access an integer value
    int column2 = (int)RadGrid1.SelectedValues["Column2"];
}