Getting the field Name in Table modified field event handler in D365

can be achieved by args.getArgNum(1);

class XXXXCustTable_EventHandler
{
    /// <summary>
    ///
    /// </summary>
    /// <param name=”args”></param>
    [PostHandlerFor(tableStr(CustTable), tableMethodStr(CustTable, modifiedField))]
    public static void CustTable_Post_modifiedField(XppPrePostArgs args)
    {
        CustTable               custTable   =  args.getThis() as CustTable;

        switch (args.getArgNum(1))
        {
            case fieldNum(custTable, CustGroup):
                if(!CustTable.OverrideSpecialMarginCode)
                {
                    custTable.SpecialMarginCode = CustGroup::find(
                                  custTable.CustGroup).SpecialMarginCode;
                }
                break;
        }
    }

}
Thanks,