"Sunk cost" is a pretty well-defined idea, we can reliably figure out whether something is a sunk cost, and whether a decision commits sunk cost fallacy, by checking whether the decision controls the amount of lost value and whether the (immutable) amount of lost value controls the decision. Skill at noticing sunk cost fallacy would then be ability to parse such situations quickly/automatically.

Testing effectiveness of training a skill is easier than testing usefulness of the skill, and I think figuring out how to train people to avoid a list of fallacies or to find correct decisions of standard kinds faster and more reliably is a reasonable goal, even if practical usefulness of having those skills remains uncertain.