var j ={"0":["75","test4","test41","ddd"],"1":["76","test5","test51","ddd"]}
var arr= [];
$.each(j,function(i,o){
    arr.push(o[2])
})
alert(arr)

------解决方案--------------------

JScript code

     var json = { "0": ["75", "test4", "test41", "ddd"], "1": ["76", "test5", "test51", "ddd"] };
     for(k in json ){
         alert(json[k][2]);
     }