PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT ?resourceType ?count
WHERE {
    {
        SELECT ("Concepts" AS ?resourceType) (COUNT(DISTINCT ?resource) AS ?count)
        WHERE {
            GRAPH ?graph {
                ?resource a skos:Concept .
            }
        }
    }
    UNION
    {
        SELECT ("Collections" AS ?resourceType) (COUNT(DISTINCT ?resource) AS ?count)
        WHERE {
            GRAPH ?graph {
                ?resource a skos:Collection .
            }
        }
    }
    UNION
    {
        SELECT ("Concept Schemes" AS ?resourceType) (COUNT(DISTINCT ?resource) AS ?count)
        WHERE {
            GRAPH ?graph {
                ?resource a skos:ConceptScheme .
            }
        }
    }
}
ORDER BY DESC(?count)