SPARQL is a Semantic Web query language that has been standardized by the World Wide Web Consortium, and a SPARQL endpoint is a Web service that answers SPARQL queries for some dataset. Semantic MediaWiki as such does not provide any such service to directly resolve SPARQL queries against the data of a wiki. Rather, it delegates the task to specialized databases that support SPARQL in an optimized fashion. To learn how to connect SMW to such databases, see Help:Using SPARQL and RDF stores.
Help:SPARQL endpoint en 1.6.0