Despite how close we are to the movie’s release, we know nothing about the location of the sixth Infinity Stone, the Soul Stone.
The Infinity War prelude comics briefly mentioned that the Soul Stone has supposedly not been seen in ages, which may explain why it has yet to appear in the films.
The only character with an Infinity Stone that didn’t make sense was the image of Iron Man within the Soul Stone.
This would explain why the Time Stone is apparently one of the first Infinity Stones Thanos goes after in Infinity War.