Let's do it one by one.
主语是you(省略)
全句应该是
You take turns asking your partner what he or she like in sandwich.
谓语是take
意思是（你们）轮流询问搭档,他或她喜欢在三明治中加什么这是什么句子啊？命令或祈使句，省略主语。像老师吩咐学生：Each 2 students make a team. Take turns asking your partner what he or she like in sandwich.