JanusGraph provides native support for the property graph data model exposed by Apache TinkerPop and uses Gremlin as its query language. It does not have native support for RDF or SPARQL. That being said, you could write custom scripts to ingest RDF and transform it into a property graph model. Daniel Kuppitz started work on transforming SPARQL queries into Gremlin, and that effort continues on at https://github.com/LITMUS-Benchmark-Suite/sparql-to-gremlin

If you are looking for something that does both, you might want to consider something like Stardog or BlazeGraph.