Decides, before and during a flight test or a launch, what happens if it goes wrong.

Every rocket launch and most flight test programmes fly over people who did not choose to be underneath them, which is what this job exists to manage. A range safety engineer analyses the trajectory, the failure modes and the debris footprint in advance, sets the destruct or termination criteria, and on the day, watches the vehicle against those limits with the authority to end the flight if it leaves the box it was cleared to fly in.
Range safety is learned on top of an engineering degree, at a specific facility, rather than taught as its own major.
Aerospace engineers · US Bureau of Labor Statistics, Occupational Outlook Handbook, May 2024 wages and 2024–34 projections.
Range safety is not tracked as its own occupation. The people who do it are almost always trained aerospace engineers, working inside the much larger figure the Handbook publishes for the discipline as a whole.
On launch day you may be the person with the authority, and the responsibility, to destroy a vehicle that took years and enormous sums of money to build, because the alternative is worse. That decision has to be made in seconds against criteria set months earlier, and being right and being fast are both required at once. The job exists because the alternative to having it has happened before.