When I get that, I just repeat the question "where did you look in the docs?", or just "go look at the docs now" if they're really dense. I can't help them until they have a better answer.

It takes a few tries before they internalize that they need to have a doc link before expecting my help. Once they do, I might take the next step to saying "here's the answer; can you update the docs so the next person doesn't have to ask?" And it might take a few tries before that sticks too. My goal is to eventually turn them into someone who evangelizes the docs themselves.

When I write peer reviews for my colleagues, I describe their attitude toward documentation. If that's "they refuse to open the docs, frequently wasting their colleagues' time", it's not gonna go well. If it's "they make nice doc edits after I ask them", a little better. If it's "they proactively maintain the documentation", better still.

Of course all this is for stuff that one could reasonably expect to be documented. Help thinking through a design problem or debugging their in-progress PR is generally a different situation.