Question: Which nation's engineers have graduated in Poland?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/education> <http://dbpedia.org/resource/Poland> . ?x <http://dbpedia.org/property/nationality> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Engineer>}