Here is the final code:
<?php
header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
$url="https://www.quandl.com/api/v3/datasets/WIKI/CNK.json?start_date=2017-11-03&end_date=2017-11-03&order=asc&transformation=rdiff&api_key=xxxx";
$content = file_get_contents($url);
$json = json_decode($content, true);
$name = $json['dataset']['name'];
$str_pos = strpos($name,"(");
$closing_price = $json['dataset']['data'];
echo 'Name '.substr($name,0, $str_pos).'<br/>';
echo 'Closing price '.$closing_price[0][4].'<br/>';
?>
solved Parsing Jason Object