1- It could be a mutation, as other diseases.
2- It could be anywhere in the world, but if I had to guess I would say preacrious countries or tropical places.
3- I'm not sure but I think they found a vaccine that actually helped.
Now, I would actually believe that AIDS came from a lab. If we look at Portugal, now there's been a lot of fires, and they are probably because of man. Some of them are actually started by firemans (the paid one's) that need money and work, because in Winter there are no fires that could pay them big. Others are started by people who use or buy wood, because burnt wood is much much cheaper (although now is prohibited its sale to end this). So, yeah, it's likley that AIDS came from a lab. The origins, Africa could be the origin, but