You can use this simple piece of code to load the K2 Extra fields in our K2 modules.

Add this code to the template file of the module:

$extraFld = array();
if ($item->extra_fields) 
{
	$extraFields = json_decode($item->extra_fields, false);
	foreach ($extraFields as $key=>$extraField)
	{
		$extraFld[ $extraField->id ] = $extraField->value;
	}
}

Now you can call a specific extra field by its id. For example:

echo $extraFld[x];

where x is the id of the extra field.

For an alternative method, check out this article.