你翻译的基本反映了句中的意思.
关于 Ph.D. scientists haven’t trained fordirectly——but for which they have useful knowledge, skills, and experience.
前一个for和but 后面的for都是目的状语,说明train的目的.
but 后面的which实际是做for的宾语,这是为了引导后面的宾语从句they have useful knowledge, skills, and experience.
也就是which是for的宾语,由于实际宾语较长,放到后面去说,也就是they have useful knowledge, skills, and experience.是一个意思.