One that has saved me many hours: given a small subset A and a disjoint sample B of a larger set of, say, complicated JSON objects in a consistent but unknown schema, what do the objects in A have in common that isn't true of any objects in B?
Example result from Claude: The field foo contains dates between August 3 and August 7, 2016 in every record in A, and every record in B contains later dates.
Claude even correctly hypothesized that it was dealing with metadata from a document management system, that field foo was the creation date of the document, and that nearby field bar, identically 10 in all records, was the document retention period in years, and thus A represented documents that would have been purged between August 3 and August 7, 2026.
One thing that helped me a ton was making an adapter between my domain specific datasets/systems and QGIS. So I can watch and examine the intermediate steps and leverage that my brain is still pretty darn good at visual pattern matching.
For what it's worth, I use duckdb and its spatial stuff as my adapter. Works for my brain and if you force e.g. SQL files for each step, gets there in the same kind of way. Still some sharp edges, mind, but overall working well. And then Claude comes for my maths and I sob.