Start here. This is the direct spoken answer to practice first.
Why this question matters
A database deadlock is a cycle: each transaction owns a resource another transaction needs. The database breaks the cycle by aborting a victim, so intermittent API failures are evidence of competing access paths rather than random SQL instability.
I capture the deadlock graph or database event and identify the victim, surviving transaction, statements, resources, and lock modes. Then I map those statements back to EF Core endpoints or jobs and inspect their transaction boundaries and generated SQL. A common case is one path updating orders then inventory while another updates inventory then orders. Making the resource order consistent and shortening both transactions removes the cycle more reliably than retries alone.