Project based but on-site for like one or two hours. Something where they consume a public api and build a UI usually a list on it. Will allow you to see their dev setup, etc... This will give you by far the most signals.
Discussions around state management, js libraries (react, vue, etc...), testing strategies (storybook, etc...) should also give you some signals too on their experience.
https://www.journable.com/