How many {demonym} are for {Africa} ?
How many African demonyms exist?
How many demonyms are there for Africa?
SELECT ( COUNT ( ?g ) AS ?c ) { resource:Africa property:demonym ?g }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q15> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1549> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q15 wdt:P1549 ?obj }
1