After John resigned, Mary was asked to take his place as team leader.

take 的意思是"拿、取"，在这里引申为"接替、承担"。 his 是代词 he 的所有格形式，指代前文提到的约翰。 place 的意思是"位置、职位"，指团队领导的职位。 take his place 是一个固定短语，意思是"接替某人的位置/职位"，即"代替某人"。