PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
SELECT count(?s)
FROM <http://www.sdi4apps.eu/poi.rdf>
WHERE {
 ?s <http://www.opengis.net/ont/geosparql#asWKT> ?geom.
 ?s geo:sfWithin <http://www.geonames.org/3175395>.
 FILTER(isBlank(?geom) = false).
 ?s ?p ?o.
}