Just start with Apache Jena, standards based with RDF as the exchange format and SPARQL for the query language. Others solutions may use proprietary stuff for better vendor lock-in: This is completely up to you if you want that. But with Apache Jena you can change later to other KG databases. Also: Apache Jena is easy to work with, since it includes Fuseki to start directly using it as a web API.

https://jena.apache.org/ https://jena.apache.org/documentation/fuseki2/

Once you need "big data" for your personal Knowledge Graph, you can use other RDF stores, without vendor lock-in.