From Facebook Developer Wiki (FbDevWiki.com)
Query this table to return the user IDs of users who like a given Facebook object (video, note, link, photo, or photo album).
Highlighted rows are indexable / searchable and one is usually required in the WHERE portion of the query.
|object_id||string||The object_id of an object on Facebook. This can be a video, note, link, photo, or photo album. Note that for photos and albums, the object_id must be queried from the photo and album FQL tables. Note that the object_id is a different field from the photo table's pid field and the album table's aid field.|
|post_id||string||The id of a post on Facebook. This can be a stream post containing a status, video, note, link, photo, or photo album. These post IDs must be queried from the stream FQL table.|
|user_id||int||The user who likes this object.|
$facebook->api_client->fql_query('SELECT user_id FROM like WHERE object_id="122706168308"');