Start here. This is the direct spoken answer to practice first.
Why this question matters
Dashboards are useful when they answer the first incident questions quickly. Decorative graphs do not help during pressure.
I would include request volume, success/error rate, p50/p95/p99 latency, top endpoints by latency and errors, dependency duration for SQL/Redis/HTTP, CPU and memory, queue age for async workflows, and recent deployment markers. I would also include one or two product-specific workflow metrics, such as successful checkouts or completed imports. That lets the owner see both technical health and whether users can finish the thing the API exists to do.