由于变量row的作用域仅在for循环内， AJAX 的回调函数是另一个作用域，因此您无法访问ajax回调函数内的变量row。要解决此问题，您可以在回调函数内定义其他变量，然后将row值赋给该新变量。

var table = document.getElementById("tab");
for (var i = 0, row; row = table.rows[i]; i++) {
   //rows would be accessed using the "row" variable assigned in the for loop
   let idd = row.cells[1].textContent;
   
   if(idd != 'Id' && idd != '') {
       $.ajax({
            type: "POST",
            url: "/numordiniperiodoagenti",
            data: {id : idd, start: sstart, end: eend},
            success: function(response){
                var target_row = row; 
                target_row.cells[10].textcontent = 'p'; //or response as it should be
            }
        });
    }
}