PREFIX     :  <http://example.org/x/>
PREFIX  rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs:  <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?x ?c
WHERE { 
?x rdf:type ?c . 
?c rdfs:subClassOf :c . 
?x :p _:y .
}
