WordPress at a glance
action is not described

comment_on_trash action-hook . WP 2.9.0

Fires when a comment is attempted on a trashed post.

Usage

add_action( 'comment_on_trash', 'action_function_name_394' );
function action_function_name_394( $comment_post_ID ){
	// action...
}
$comment_post_ID(int)
Post ID.

Where the hook is called

wp_handle_comment_submission()
wp-includes/comment.php 3038
do_action( 'comment_on_trash', $comment_post_ID );

Where the hook is used (in WP core)

Does not used.