Part of the job of a mentor/senior engineer is spending time helping get juniors up-to-speed on projects and getting them comfortable asking questions. And if they're not asking questions, checking in on them to see how they're doing. (Pro-tip: don't just ask them how they're doing, have them explain what they're doing and why. Problems show up a lot faster that way. :)

Building an environment where junior engineers learn how to find things out on their own and when they need to ask questions is a company culture thing and has very little to do with remote vs in-office.