Interview for a PhD position at a German university
I currently work in Germany, and have exactly the situation xLeitix mentions in his comments: I have positions which I am able to choose directly who I want to hire, independent of any admissions committee.

In such interviews, I want to have a sense of the student's technical prowess, as well as a sense of their motivation and interest in the position itself. Since such positions are usually directly associated with particular projects, I want to make sure that the candidate is reasonably qualified to tackle the specific project (rather than just being generally competent in the field).