Scheduled reminders
Design a reminder/scheduled-task feature for a small to-do app. A user sets a reminder for a task at a specific future time, and when that time arrives the system sends them a notification. Reminders can be minutes or weeks out; volume is modest. Describe how you store scheduled reminders and how the system fires them at the right time.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify3:30 left
Estimate3:30 planned
Design10:00 planned
Deep dive8:00 planned
Failure5:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.