On which of the planets (other than earth) could a human being step out of a spacecraft and survive without any protective gear (special suit, oxygen tanks, etc)?

There isn´t other planet on which we could survive unprotected

Explanation:

Still no other planet has been found that has an atmosphere capable of retaining oxygen and decreasing solar radiation so that the person does not need as much oxygen equipment as a special suit to avoid the different types of raciations that can reach the planet .

It is also believed that it is possible to find on a future planet similar to Earth in which you can live without protection.

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.