Why is this SPARQL query returning an empty result?

Question

SPARQL

I am learning to make queries, I form a query in Protege on SPARQL

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT * WHERE {
?a rdfs:SubClassOf <http://www.semanticweb.org/ugrobug/ontologies/2021/2/untitled-ontology-16/Rock>;
}

Gives an empty result. I open the ontology and there is a record.

<SubClassOf>
        <Class IRI="#Symphonic_rock"/>
        <Class IRI="#Rock"/>
    </SubClassOf>

Why doesn't it work?