Getting the profile2 user fields?
It seems like you want to retrieve the value of a single field from a field collection. And that the field collection you want to retrieve a field from is a field of a 'cv' profile2.

The returned value of profile2_load_by_user($account, "cv"); is a Profile entity object. When $fieldset is the (machine) name of a field collection field, then you can retrieve its value using $items = field_get_items('profile2', $profile, $fieldset) (see field_get_items()). This will return an array of field collection values (or FALSE if there is no value for the field). The values are arrays containing a value entry which is the entity id of a field collection entity. You can load the field collection entity for an ID using field_collection_field_get_entity(). Finally, using $key as field name, you can retrieve the values of one of this field collection entity's fields using field_get_items() again.

$items = field_get_items('profile2', $profile, $fieldset);
if ($items) {
  $item = reset($items);
  if (!empty($item['value'])) {
    $field_collection = field_collection_field_get_entity($item);
    if ($field_collection) {
      $items = field_get_items('field_collection', $field_collection, $key);
      if ($items) {
        $item = reset($items);
        return !empty($item['value']) ? $item['value'] : 0;
      }
    }
  }
}
return 0;