When to use it
Use it after a presentation, project or meeting where you'd like to improve. A specific question gets a specific answer. “Any feedback?” usually gets “Looked good!” which doesn't help you grow.
Example
You: “What's one thing I could do differently in my next presentation?”
Manager: “Slow down on the numbers slide. That's where people needed more time.”
In an email or Slack message
By message: “Thanks for coming to the review. What's one thing I could do differently next time?” Asking for one thing makes it easy to answer.