How to list comments of certain node in a PHP
You can use the Views module to create custom lists of nodes, comments, users etc. In your case, you will need to:


create a view of comments
add a 'Feed' display
add a 'Contextual filter' for 'Comment: Nid' (this will allow you to specify the node ID in the url)
set the feed url to something like comments/%/rss, where the % is a placeholder for the Node ID
save the view


Now you can find an rss feed of comments for node 32 at http://example.com/comments/32/rss

Here is an export of such a view:

$view = new view;
$view-&gt;name = 'comments_rss';
$view-&gt;description = '';
$view-&gt;tag = 'default';
$view-&gt;base_table = 'comment';
$view-&gt;human_name = 'comments rss';
$view-&gt;core = 7;
$view-&gt;api_version = '3.0-alpha1';
$view-&gt;disabled = FALSE; /* Edit this to true to make a default view disabled initially */

/* Display: Master */
$handler = $view-&gt;new_display('default', 'Master', 'default');
$handler-&gt;display-&gt;display_options['title'] = 'comments rss';
$handler-&gt;display-&gt;display_options['access']['type'] = 'perm';
$handler-&gt;display-&gt;display_options['cache']['type'] = 'none';
$handler-&gt;display-&gt;display_options['query']['type'] = 'views_query';
$handler-&gt;display-&gt;display_options['query']['options']['query_comment'] = FALSE;
$handler-&gt;display-&gt;display_options['exposed_form']['type'] = 'basic';
$handler-&gt;display-&gt;display_options['pager']['type'] = 'full';
$handler-&gt;display-&gt;display_options['pager']['options']['items_per_page'] = '10';
$handler-&gt;display-&gt;display_options['style_plugin'] = 'default';
$handler-&gt;display-&gt;display_options['row_plugin'] = 'comment';
/* Relationship: Comment: Content */
$handler-&gt;display-&gt;display_options['relationships']['nid']['id'] = 'nid';
$handler-&gt;display-&gt;display_options['relationships']['nid']['table'] = 'comment';
$handler-&gt;display-&gt;display_options['relationships']['nid']['field'] = 'nid';
$handler-&gt;display-&gt;display_options['relationships']['nid']['required'] = 1;
/* Field: Comment: Title */
$handler-&gt;display-&gt;display_options['fields']['subject']['id'] = 'subject';
$handler-&gt;display-&gt;display_options['fields']['subject']['table'] = 'comment';
$handler-&gt;display-&gt;display_options['fields']['subject']['field'] = 'subject';
$handler-&gt;display-&gt;display_options['fields']['subject']['label'] = '';
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['alter_text'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['make_link'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['absolute'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['word_boundary'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['ellipsis'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['strip_tags'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['trim'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['alter']['html'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['hide_empty'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['empty_zero'] = 0;
$handler-&gt;display-&gt;display_options['fields']['subject']['link_to_comment'] = 1;
/* Sort criterion: Comment: Post date */
$handler-&gt;display-&gt;display_options['sorts']['created']['id'] = 'created';
$handler-&gt;display-&gt;display_options['sorts']['created']['table'] = 'comment';
$handler-&gt;display-&gt;display_options['sorts']['created']['field'] = 'created';
$handler-&gt;display-&gt;display_options['sorts']['created']['order'] = 'DESC';
/* Contextual filter: Comment: Nid */
$handler-&gt;display-&gt;display_options['arguments']['nid']['id'] = 'nid';
$handler-&gt;display-&gt;display_options['arguments']['nid']['table'] = 'comment';
$handler-&gt;display-&gt;display_options['arguments']['nid']['field'] = 'nid';
$handler-&gt;display-&gt;display_options['arguments']['nid']['default_action'] = 'not found';
$handler-&gt;display-&gt;display_options['arguments']['nid']['default_argument_type'] = 'fixed';
$handler-&gt;display-&gt;display_options['arguments']['nid']['default_argument_skip_url'] = 0;
$handler-&gt;display-&gt;display_options['arguments']['nid']['summary']['number_of_records'] = '0';
$handler-&gt;display-&gt;display_options['arguments']['nid']['summary']['format'] = 'default_summary';
$handler-&gt;display-&gt;display_options['arguments']['nid']['summary_options']['items_per_page'] = '25';
$handler-&gt;display-&gt;display_options['arguments']['nid']['break_phrase'] = 0;
$handler-&gt;display-&gt;display_options['arguments']['nid']['not'] = 0;
/* Filter criterion: Comment: Approved */
$handler-&gt;display-&gt;display_options['filters']['status']['id'] = 'status';
$handler-&gt;display-&gt;display_options['filters']['status']['table'] = 'comment';
$handler-&gt;display-&gt;display_options['filters']['status']['field'] = 'status';
$handler-&gt;display-&gt;display_options['filters']['status']['value'] = 1;
$handler-&gt;display-&gt;display_options['filters']['status']['group'] = 0;
$handler-&gt;display-&gt;display_options['filters']['status']['expose']['operator'] = FALSE;
/* Filter criterion: Content: Published */
$handler-&gt;display-&gt;display_options['filters']['status_node']['id'] = 'status_node';
$handler-&gt;display-&gt;display_options['filters']['status_node']['table'] = 'node';
$handler-&gt;display-&gt;display_options['filters']['status_node']['field'] = 'status';
$handler-&gt;display-&gt;display_options['filters']['status_node']['relationship'] = 'nid';
$handler-&gt;display-&gt;display_options['filters']['status_node']['value'] = 1;
$handler-&gt;display-&gt;display_options['filters']['status_node']['group'] = 0;
$handler-&gt;display-&gt;display_options['filters']['status_node']['expose']['operator'] = FALSE;

/* Display: Page */
$handler = $view-&gt;new_display('page', 'Page', 'page');
$handler-&gt;display-&gt;display_options['path'] = 'comments/%';

/* Display: Feed */
$handler = $view-&gt;new_display('feed', 'Feed', 'feed');
$handler-&gt;display-&gt;display_options['pager']['type'] = 'some';
$handler-&gt;display-&gt;display_options['style_plugin'] = 'rss';
$handler-&gt;display-&gt;display_options['row_plugin'] = 'comment_rss';
$handler-&gt;display-&gt;display_options['path'] = 'comments/%/rss';
$handler-&gt;display-&gt;display_options['displays'] = array(
  'default' =&gt; 'default',
  'page' =&gt; 'page',
);