使用this引用

$('.filename img').click(function () {
   $(this).parent().next(".datalog").show();
});

解释

$(this)-->current clicked element , which is img
parent()--> go to parent which is `li`
.next(".datalog") --> go to the next element whose class is `.datalog`, that is `ul` 
.show()  -->show

fiddle here

你可以这样做：

$('.filename img').click(function () {
    $(this)                   // Get the current img being clicked
         .closest('li')       // Go to the closest parent `li` to the img
         .next('.datalog')    // Go to the next sibling of the `li`
         .show();             // Show the `ul` with the class `.datalog`
});

FIDDLE DEMO #1
你也可以试试这个：

$('.filename img').click(function () {
    $(this).closest('li').next('.datalog').show().siblings('.datalog').hide();
});

FIDDLE DEMO #2

$('.filename img').click(function () {
    $(this).closest('li').next(".datalog").show();
});

演示---->http://jsfiddle.net/Lnxdf/2/

http://jsfiddle.net/Lnxdf/9/

$('.filename img').click(function () {
    $(this).parent().next('ul.datalog').show();
});

虽然我不太喜欢这样的结构

使用此代码：

$('.filename img').click(function () {
    $(this).parent().next().show();
});

http://jsfiddle.net/Lnxdf/6/

尝试此完整过程

$(document).ready(function(){

    $('.filename img').click(function () {
        if( $(this).closest('li').next('.datalog').is(':hidden')) {
        $(this)                   // Get the current img being clicked
             .closest('li')       // Go to the closest parent `li` to the img
             .next('.datalog')    // Go to the next sibling of the `li`
             .show();             // Show the `ul` with the class `.datalog`
        } else {
               $(this)                   // Get the current img being clicked
             .closest('li')       // Go to the closest parent `li` to the img
             .next('.datalog')    // Go to the next sibling of the `li`
             .hide();             // Show the `ul` with the class `.datalog`
        }
    });
});