I have been working on this. I was able to see my friend's friends.
To do this, the following requirements are required:
- Your friend should use the app.
- Permission from the application read_stream, publish_stream, publish_checkins.
Try this fql query.
$query="SELECT uid, name, work_history FROM user WHERE uid IN (SELECT uid2 FROM friend WHERE uid1 IN ( SELECT uid FROM user WHERE uid IN (SELECT uid2 FROM friend WHERE uid1 = $fb_id ) and is_app_user=1) )";
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