1.He didn't become a person who his father wanted him to be .在这个定语从句中,先行词是person,关系代词是who,从句的主语是his father,宾语是him,who做表语,逻辑上是his father wanted him to be who.
2,The boy who I know studies best in his class 中,studies 是主句的谓语,当然取决于主句的主语,主句的主语是the boy,三单,故用了studies.一般来讲,这与先行词无关的.只不过这里的先行词刚好就是主语.
此外,定语从句的谓语动词的单复数要跟先行词一致的.至于时态,则要看从句具体表达的语境来定.从句的时态与主句的时态并无直接的关系,是互相独立的.
祝你进步.