How to print "rendered node" version of Node Reference field in template?
In your $node object, you will find the subordinate node object at $node-&gt;field_fieldname['und'][0]['node']. To render this in a page you have to turn it into a renderable array. You do this with node_view(),specifying the type of display mode. Try:

&lt;?php
if(isset($node-&gt;field_fieldname['und'][0]['node'])) {
  $second_node = $node-&gt;field_fieldname['und'][0]['node'];
  $view_mode = 'teaser'; // or 'full' as the case may be
  $render_array = node_view( $second_node, $view_mode);
  print render($render_array);
}
?&gt;


EDIT 

MPD is correct. The above assumes that the field is a Node Reference field. If you are using an Entity Reference field, the code should be changed to:

 &lt;?php
    if(isset($node-&gt;field_fieldname['und'][0]['entity'])) {
      $second_node = $node-&gt;field_fieldname['und'][0]['entity'];
      ...