If you want to return all the fields of a field group you can use
$fields = acf_get_fields($group_key);
if you want to get all the field groups for a post
$groups = acf_get_field_groups(array('post_id' => $post_id));
putting them together
$groups = acf_get_field_groups(array('post_id' => $post_id));
if ($groups) {
foreach ($groups as $index => $group) {
$groups[$index]['fields'] = acf_get_fields($group['key']);
}
}
echo '<pre>'; print_r($groups); echo '<pre>';