How to add Flag to a rendered View
Just a single flag for the rendered page view that displays all
  articles (i.e., a way to bookmark the "read all news" page.)


ok then doing it the way you were doing it, is the way to go.

$node-&gt;nid alone won't return the nid, you need to to use menu_get_object() function

&lt;?php

if ($node = menu_get_object()) {
  // Get the nid
  $nid = $node-&gt;nid;

print flag_create_link('bookmarks', $nid);

}

?&gt;


Note 1: If you're using a page view, the above won't work since it cannot fetch an nid since page view's don't have node id's. In order to get it to work, you can create a block view, and then create a node where you insert your block view. Then since the node has a nid, it's able to fetch the node id. 

Note 2: You can ignore all the comments below, as they were due to using a page view (see note1)