List of Collection attributes

   * content
   * description

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX sioc: <http://rdfs.org/sioc/ns#>
SELECT distinct ?attribute
FROM <http://demo.openlinksw.com/Doc>
WHERE 
  {
    ?forum a sioc:Container .
    ?forum sioc:is_collection_of ?collection.
    ?collection ?attribute ?o  
   }

Sample Data (Live Query Results)

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