Responsible, experienced engineers should teach newcomers that experiencing self-doubt is part of the process in maturing. I had the fortune to work under a mentor in my original position in this company that wasn't afraid to pull his assigns in to help solve problems he was working on.
Seeing that people of his caliber still acknowledge the value of second opinions and eyes really helped me understand that this business is not about the individual bodies entombed in cube walls, but a complex effort of many teammates.
After I embraced that, I learned where I could, and contributed where I could, and I personally feel much more productive as a member of my new team because of that. Do I still feel like I don't know things? Definitely. I also know that it's a big field and we all won't know everything.
My next goal is to find my way to a leadership position so I can perpetuate this kind of mentality downwards.
If we pretend for a moment that hiring processes are perfect methods for identifying the top X% of candidates objectively, when you are hired by a company that only hires the top 10% of candidates, when you are hired, you instantly go from being better than 90% of your cohort to being average. You might go from being in the 92nd percentile of your old cohort to the 20th percentile of your new cohort.
Sure, it's less stark when hiring processes aren't perfect and hiring criteria are fuzzy and don't oerfectly match the actual job requirements, but any time you go through a selective process it's going to happen a little.
Impostor Syndrome is, or has, become like Asperger's, where every dev thinks they have it. It's a "humblebrag". I honestly tell people I mentor, be confident, but humble. You have this job because you're qualified (or you made yourself qualified), so have confidence in your skills - sit up right, answer questions, take ownership. But also be humble. Don't be afraid to say I don't know, admit you don't know everything about developing.
It's OK To say "I don't know, but I'm doing my best, and if I did, I could answer you."