Final answer:
Herbert Hoover, who served as the 31st President of the United States during the rise of the Nazi Party, is the person among the options given who witnessed their ascent while abroad.
Step-by-step explanation:
Of the three individuals mentioned, Herbert Hoover witnessed the rise of the Nazi Party while he was abroad. Herbert Hoover served as the 31st President of the United States from 1929 to 1933, a period which encompassed the early years of the Nazi Party's ascent to power in Germany. Hoover was in office during a time of great economic turmoil known as the Great Depression, which also affected Germany and contributed to the political conditions favorable for the Nazi Party's growth.
Unlike Hoover, Paul Robeson and Tessie Mobley were not in political office during this time and are not noted for witnessing the rise of the Nazi Party while abroad.