I’m quite sure we dont have anything related to the Query exec part by part but we have this
Which helps you understand how the Query is processed in the Cluster.
You can also check the paper Dgraph Whitepapers: In-Depth Insights and Analysis
You can also learn a lot from Jaeger tracing https://dgraph.io/docs/deploy/tracing/
If you set up the Jaeger with Dgraph cluster getting like 99% of the calls. You can see the query execution. It wont teach you about syntax or something. But you may understand something in the process.