world-class = elite level performance
gun against your head = hyper-accelerated implementation
A fascinating question. I'm going to enjoy putting the same question to friends.
I initially thought about quantum mechanics (despite being a biologist I've always been intrigued by high level physics) but the desire that percolated after a time in my thoughts was linguistics. I'm bilingual and can appreciate the extent of nuance lost in translation as well as the richness of culture, history, learning, and the social and commercial opportunities that are possible with the level of communication that fluency in another language enables. So the answer to the first part of the question is the ability to learn another language at a very high level of competence.
The answer to the second part of the question, however, is what I suspect you're probably most interested in. It certainly is the more intriguing.
During exam preparation (in what seems like eons ago now) I did develop a methodology for rapidly absorbing vast amounts of information in very short periods of time. It involved mind maps, mnemonics, repetition, exercise, chewing gum, stimulants, talking aloud to one self, short sleeps, short breaks, a low carb diet and a multi-sensory immersion in the topic. It worked but I couldn't have anyone around me during this period, or take calls or interact in any way.
In effect, I entered a hyper-vigilant, hyper-focused state that was difficult to maintain but enabled rapid learning. There was one other proviso, the material preparation was a key factor in that it had to be 'processed' in a way that made it easy to assimilate, i.e. learn. The processing involved something like breaking information down into singular concepts that could be linked into pre-existing knowledge.
In short, the material was prepared and then I would enter into an appropriate state to learn it. Sort of like the mastication, digestion and absorption of information. And that, I hope, forms the answer to the second part of your question.