Based on the fact that sorters returns a value which appears to be equal to another field in the model, you wish to dynamically return that field.

There's a few ways to do this, probably the best is to provide the variable option when creating the template (docs). See example below:

var model = new Backbone.Model({
  name: "P",
  surname: "a",
  sorters: ["name","surname"]
});

var tmp = _.template($('#template').html(), {variable: 'data'});
$('#result').html(tmp(model.attributes));

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/backbone.js/1.3.3/backbone-min.js"></script>
<script id="template" type="text/template">
<% for(i=0; i < data.sorters.length; i++ ){ %>
   <h2><%= data[data.sorters[i]] %></h2>
<% } %>
</script>
<div id="result"/>

Also, better to use each rather than a for loop:

<% _.each(data.sorters, function(sorter) { %>
   <h2><%= data[sorter] %></h2>
<% }) %>