IMHO, Oaks would be in charge of legal (we all know ChurchCo is virtually judgment-proof, but I'm betting they sue others such as contractors, suppliers, etc.
Had I stayed the course and allowed destiny to float me to the top, like a fine mocha cream, I would probably have been in charge of catering the temple meals.
There was a time when the apostles had specific assignments such as mission presidents, temple presidents, overseeing sunday school or church education. I think that time has long passed.
I believe that they are assigned to certain areas of the church and have to travel to certain areas of the world. In addition to meeting as the Q15, I believe that they meet with other members of the Q70, area presidents and regional reps. I think the modern church is a giant bureaucracy similar to Congress and their committee work.