Quick answer
For the dwelling itself: construction specifications or blueprints if available, details on any custom features or high-end finishes, and the date of any major renovations. For valuables: current appraisals for fine art, jewelry, and collections, along with receipts or provenance documentation where you have them. For liability: a general picture of your net worth and any specific exposures, rental property, a pool, domestic staff, that affect umbrella sizing.
None of this needs to be perfectly organized before you call. Part of what a full asset review does is help identify what’s missing and get it gathered, rather than requiring a complete file upfront.