Dgraph supports only N-triples. No fancy RDF formats.
I’m not sure if Prótége has N-triples exporter, it has CSV exporter for sure. What you can do is “Save as” json-ld. And you can sanitize it a bit. As you can see https://github.com/dgraph-io/dgraph/issues/4897 Dgraph don’t fully support JSON-LD due some conflicts with internal keywords.
One thing you have to pay attention to is that Dgraph does not support ontology. That is, you need to treat/sanitize this dataset before inserting it into Dgraph - and you can “simulate” ontology if you are a advanced user of
GraphQL+-. There are several approaches you can take. Always remembering that Dgraph is an N-triple DB, but it is not really a triple store (as is the case with DBs that support ontology).
BTW, there is other cool tool called “OpenRefine” former “Google Refine”. You can import several formats and “refine/sanitize” it. And you can export it to JSON. In “Export => Templating”.
This tool is good to create JSON from CSV or spreadsheets too.
But you need to lear how to use the Refine queries to treat/refine/sanitize the data.
PS. You can use https://json-ld.org/playground/ to transform JSON-LD into triples. Paste the JSON-LD in the input box, and go to N-Quads tab.