I had a skim through the RDF* spec, but I didn't see any diagrams. I guess it would be similar to the diagrams in, say, https://www.w3.org/2018/09/rdf-data-viz/. I can see there are a few different concrete syntaxes defined. Although just defining (A, B, C) as equivalent to "node A; node C; A -> C : B" gets a lot of the way there. But I'm not clear what ((A, B, C), D, (E, F, G)) would look like. Edit: the link in the comment below solves this by making the comment on the arrow an addressable node.
Another source may be of some help:
https://www.ontotext.com/knowledgehub/fundamentals/what-is-rdf-star/
Do you think Plantuml is suitable for displaying RDF* data?
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about RDF*, please have a look at:
https://enterprise-knowledge.com/rdf-what-is-it-and-why-do-i-need-it/
wish it helps.