答：作狀語（不壹定只是時間、地點原因）或定語。（可理解成介詞短語在句中充當成分）
例子：
I don't like the way in which you talk to your father.我不喜歡妳跟妳爸說話的方式。
in which=in the way（這裏是作方式狀語）
There are ten books here, two of which belong to you. 這裏有十本書，其中兩本是妳的。
(of which 這裏是定語)
所以，在They are the possessions of the autonomous(self-governing) man of traditional theory, and they are essential to practices in which a person is held responsible for his conduct and given credit for his achievements.
中的in which=in the practices，其實就是地點狀語。（在實踐中）（指明範圍）
譯文：
它們是傳統理論中自主(自治)的人的財產，是實踐中必不可少的，在實踐中，壹個人要為他的行為負責，並為他的成就受到贊揚。（翻譯來自有道詞典）