Glossary
knowledgeC.db
knowledgeC.db is the CoreDuet SQLite database where macOS logs user and device activity such as app usage, focus and display state over time.
knowledgeC.db is a SQLite database maintained by Apple's CoreDuet framework to record user and device activity for features such as Siri suggestions and Screen Time. On macOS it exists at a system location (/private/var/db/CoreDuet/Knowledge/knowledgeC.db) and per user (~/Library/Application Support/Knowledge/knowledgeC.db).
Events live mainly in the ZOBJECT table, grouped by ZSTREAMNAME values such as /app/usage or /app/inFocus, with start and end dates stored in Mac Absolute Time. The available streams vary by macOS version.
On recent releases Apple has shifted much of this telemetry to Biome, so knowledgeC.db may be sparse or incomplete. Read knowledgeC and Biome for queries and caveats.