Are backlinks embeded into articles from https://www.quora.com/ and http://www.linkedin.com/ do-follow?
Quora: rel="noopener nofollow" Linkedin: Both dofollow and nofollow. Depends on where those links appear. If it's a link within your profile, it will be dofollow.
Both no-follow I believe, but you want their TRAFFIC and eyeballs clicking on your links so write an amazing piece of content with images and embedded video and you'll get lots of traffic from it. Same for Reddit and Medium.
Here you can see which websites are dofollow and which - nofollow https://www.slideshare.net/DSIM2014/list-of-do-follow-websites-used-to-build-backlinks
Yes, dear, the links from both Quora and LinkedIn are nofollow. But the good news is that... these nofollow links are better than average dofollow links for SEO effect. Let me know if you need an explanation.