In general, you CAN'T get the email address of your friends (source):
User permission Friends permission
email not available
BUT but since your friend has authorized your application, you can try the following in the FQL console:
SELECT email FROM user WHERE uid=FRIEND_ID
What I suspect the problem could be is that you need the "friend's" access_token
to actually get the email because I suppose you are logged-in as your user when trying your query. So you need to grant the offline_access
permission and then use it with the query.
But before doing the above, I would try it with an application access_token
.
P.S: the sub-query is not needed if you know the friend id.
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