Any topic that involves advanced maths or other hard science will be hard to pick up quickly (despite doing a Physics degree), but other than those, most business-related activities tend to be fairly straightforward to pick up, so long as you have the right "learning materials" (be it work samples, manuals, people to coach you, whatever makes sense for the activity).

Sure, there's a world of difference between "being productive" and "being an expert", but again, I'm not saying you can become an expert in a week, I'm saying you can be productive.

Moreover, I'd argue that with the right coaching/motivation/environment, most smart people can do this.