I have learned SPARQL to do query over DBpedia, but since I finished the course, I found that I am not able to write query on https://dbpedia.org/sparql, because I do not know the the RDF format for the page.
I want a link for learning query over Virtuoso, or a way to find the RDF source of DBpedia.
You might start with a resource description page on DBpedia...
Or the Facet Browser...
Or the iSPARQL graphical query builder...