How do I grant edit access on workbench to specific users?
I solved my problem as follows:
1) Using hook_views_query_alter I fetched the desired rows. With that step I was able to see in the recent content list all the rows I want but with edit link only to the ones that the logged in user has created.
In order to see the edit to the rest of the rows whose author is somenone else I followed the step 2.

switch ($view-&gt;name) {
case "workbench_recent_content":
...
unset($query-&gt;where);
....
$where_expression = MY where statement where I filtered by content type and by a field_location field that exists on all of my content type.
 $query-&gt;add_where_expression(0, $where_expression);


2) I created a rule, on node save, grant edit access to the people that have a specific role and belong to a specific country. That way the edit link appeared even all the rows I wanted.