How do you self-teach yourself about a field you don't know about, specifically for STEM? When I was in an undergrad, I joined a DNA nanotechnology lab and the assistant professor who was member of the lab gave me bunch of papers to read to get acquainted with the field. When I joined a computational physics lab, it was the same and the professor gave me a paper to read. I do understand that, in labs, you don't have textbooks but bunch of papers to teach yourself.

I am curious about how people in academia self-teach themselves about a field they don't know about. Would they read a review from major peer-reviewed journals, such as Science or Nature, and then dig deeper from there? How would they get teach themselves techniques, and knowledge? When I was in a lab, I didn't have to worry about those things since professors gave me things I needed to read. But, if there was no person like that, how would the researcher get acquainted with the field?
Would they read a review from major peer-reviewed journals, such as Science or Nature, and then dig deeper from there?


Yes.


  How would they get teach themselves techniques, and knowledge?


Techniques can also be learned from journal articles, but it's also typical to defer to or collaborate with other researchers who are more familiar with those techniques, or to travel and visit labs. In my personal experience, several times contacts at conferences etc led to communication between labs. The lab I worked in during grad school a few times hosted grad students from other labs both inside and outside our institution that spent a few days or hours here to see how we did a particular thing, and similarly people from our lab would travel around.

When academics travel to give talks at other universities, one of the key parts of their visit is to tour other labs, which can include observing techniques used by those labs.

I'd add that this doesn't just apply to new or unfamiliar techniques, either: it's part of the normal art of improving research methodology.

More broadly, though, mid- and later-career academics don't tend to move from field to field arbitrarily (whereas it's not uncommon to make a big jump between undergrad and grad school: you simply aren't that committed to a field at that point): they usually have some adjacent knowledge that's taking them into that area, so they aren't starting completely from scratch.