句型“你认为……怎么样”：1.how do you like sth.?2.how do you find sth.? 3.what do you think of sth.?
所以这句话应该翻译为：那个海外留学生认为美国人怎么样?（the student abroad很明显是单数,特指前文提到的"那个留学生"）
英语可以改成：What does the student abroad think of American people?或者How does the student abroad like American people?如果非要说How does the student abroad think of American people?也能听懂,但是最好不要这样说