I've not heard of SPARQL, after digging around the wiki page it looks like it's a good idea which hasn't caught on much (of the top graph 5 databases [0] only Virtuoso supports it). What I find particularly interesting is it appears to be a universal query language, to replace SQL and XQuery too.. so we should be seeing it used everywhere.

With respect to graph databases, the industry standard is Tinkerpop-Gremlin. Of the top 5 graph databases 4 support it, coincidentally the only one not to support it is Virtuoso. It's not like any other query language I've used, there's quite a bit of learning involved and the docs[1] sometimes lack sufficient detail, there's multiple ways of achieving the same result and unfortunately, some implementations don't provide the full language (eg Cosmos Graph [2] doesn't support the Match step or lambdas). But slowly with handy resources like (Practical Gremlin)[3] and trial and error, you can do some very sophisticated things.

[0]: https://db-engines.com/en/ranking/graph+dbms [1]: https://tinkerpop.apache.org/docs/3.5.1/reference/ [2]: https://docs.microsoft.com/en-us/azure/cosmos-db/gremlin-sup... [3]: http://www.kelvinlawrence.net/book/PracticalGremlin.html