How many {interested in} are to/by {nationalism} ?
Nationalism interests what number of people?
How many are interested in nationalism?
SELECT ( COUNT ( ?b ) AS ?k ) { ?b property:interested_in resource:nationalism }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P2650> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q6235 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P2650 wd:Q6235 }
26