What is the name of the person who is assigned to train the new missionary?
The Best Two Years portrays the experience of four missionaries of The Church of Jesus Christ of Latter-day Saints living in the same apartment in Haarlem in the Netherlands.  The movie begins with Elder Rogers finding out that his new companion will be a "greenie", a newly trained missionary fresh from the Missionary Training Center.  He and the other two missionaries that reside in the same apartment, Elder Johnson and Elder Van Pelt, go to the train station to meet the new elder.  Elder Rogers finds out that the new missionary, Elder Calhoun, is exactly what he had jokingly predicted his new companion would be like.
Elder Rogers used to be an excellent missionary, until his girlfriend married one of his former mission companions.  That is why he and the other two missionaries residing in the same apartment are surprised that the mission president has assigned him to be the trainer (first companion and mentor) to a missionary new to the mission.
The new missionary, Elder Calhoun, tackles mission work with unbounded enthusiasm.  He attempts to talk to anyone although he has little knowledge of the Dutch language.  Despite his poor Dutch, he continues to have an eager attitude.
Fortunately for him, he soon encounters a man from the United States that speaks English.  They speak briefly in the park before the man goes off with his girlfriend.  Later, when he encounters the same man in a market, Calhoun gives him a Dutch Book of Mormon with his telephone number.  Despite what the other three missionaries expect, the man does call and asks for Calhoun.
Elder Rogers