Interviewers ask career motivation questions to determine why you want to work for their company and why you want to work in role to which you have applied. Career motivation questions are similar to, but not the same as commitment to career questions and are often used as part of a competency based interview.
You need to logically illustrate your desire to work for the company you are interviewing with. Good answers should make reference to any: training, qualifications and/or experience that you would receive, if you were to be offered the role you have applied for.
Career motivation questions you may be asked include:
Now see - Competency Based Questions and Competency Based Interview or ask a question on the WikiJob forums.