Two timed sessions, on your own or with a friend playing the interviewer.
Mock 1 — live coding, 40 minutes. Build a screen from a one-paragraph description: a list loaded from JSON, with a detail screen and a loading state. Narrate your decisions as you type. Afterwards, write down every place you hesitated.
Mock 2 — explain a design, 30 minutes. Take a screen from the Trips app and explain, out loud and without notes, where each piece of state lives, who owns it, and why. Record yourself. Listen for the places where you were vague.