> How exactly would they go about and test if it works on humans?
Presumably, the same as the other HIV vaccines that are in trials.
> Are there people who volunteer to get infected with HIV?
There are people who volunteer for vaccine trials. They don't need to volunteer to get infected with HIV -- basically, you get a large enough experimental and control group, study risk factors in the groups, and track infection rates, and evaluate whether, based on that, the vaccine reduces infection rates.
Presumably, the same as the other HIV vaccines that are in trials.
> Are there people who volunteer to get infected with HIV?
There are people who volunteer for vaccine trials. They don't need to volunteer to get infected with HIV -- basically, you get a large enough experimental and control group, study risk factors in the groups, and track infection rates, and evaluate whether, based on that, the vaccine reduces infection rates.