There is no designated visiting team sections as opposing team fans can sit anywhere they please. The visitor dugout is on the third base side, so sitting on that side will be closer to the away team. Sitting right behind the dugout is ideal because then you have a great view of the players in the on-deck circle and when they come out of the dugout.

Visitor dugout at Target Field
Sections 10-14 are great options for visiting team fans due to their location behind the visitors dugout