We are hiring a bunch of Node.js developers at the moment. You may be as well. I'm sure you have a good list of skills that you're looking for in developers that join your posse. Here are a few technical things I think about when getting the opportunity to sit down with a Node developer.
What might you add to the list?
What are options for async flow control? Favorites? Least? Pros? Cons?
Node event loop -- How does it work? What applications does it fit?
Limitations/advantages in handling async errors?
Handle errors in Promises?
Handle errors in callbacks?
What errors should be thrown?
What is immutability? Why want it?
Basic Array.prototype methods?
What does shared state give you?
Advantages to pure functions?
Applications of higher-order functions?
Specifically, how does CORS work?
Familiar with which request and response formats? Favorite? Worst? Why?
How does middleware work? When do you like to use it?
How can you use all CPUs on a server?
How to associate logs together with a single request path?
How to recover from fatal errors?
How do you load per-environment configuration?
How do you handle versioning of your apps and libs?
Why use modules?
How do you organize your API apps' modules?
Flavors of exports? When do use each?
Which new features have you used? Like, not like?
async/await - Used instead of what?
Object literal extensions - How used?
Spread operator - Helpful usecases?
Arrow functions - What do they help with?