I've been mentoring a few people starting or early in their product design (UX/UI/etc.) career.

Any advice for people starting their career on how to begin building a portfolio that can ultimately land them a job (that hopefully doesn't involve working for free)?

you can have them work on mock projects of their own? or check out catchafire - where they could work for free but for nonprofits so it isn’t as bad. maybe you can group them up and have a designathon one week challenge where they need to come up with a full blown project?

The job board here on Posts seems to have a floor of "Senior". Wondering where a newcomer might look to.

Networking. So many of the jobs I got as a freelancer happened from knowing people and putting myself out there — unfortunately I’ve heard so often “I’d rather work / hire someone I know!” for small jobs.