The OMA SPARQL endpoint is reachable by using your preferable programming language or SPARQL interface through the following URL address: https://sparql.omabrowser.org/sparql.
The OMA SPARQL endpoint is updated in sync with the OMA Browser. The data of the current release as well of the previous releases can be downloaded from the download section of the OMA Browser as turtle files (look out for OMA Browser in RDF).
The RDF serialisation of the OMA Hierarchical Orthologous Groups is based on the ORTH ontology specification in the context of the Quest for Orthologs (QfO) consortium (see GitHub repository here).
To cross-reference other resources, this SPARQL endpoint contains annotation property assertions defined by a first draft of the life-sciences cross-reference (LSCR) ontology that is available to download at the Quest for Orthologs github repository here - lscr.ttl file.
You can check if an endpoint contains the necessary metadata here.