There is no field in manage display of content type to display Flag link.
There is a tpl file (node--article--teaser
node--article--teaser.tpl.php) for teaser mode displaying bookmark
<?php if (isset($content['links']['flag'])) : ?>
<?php echo render($content['links']['flag']);?>
<?php endif; ?>
But for another mode this having View mode teaser_2_col and tpl file name node--teaser-2-col
node--teaser-2-col.tpl.php, $content['links']
does not have a Flag element.