Motivation is unique. It is personal. Some people are motivated by money; others are motivated by things such as interesting work, supportive environment, competitive environment, recognition, training and development opportunities, and the reputation of the organization.
Whatever it is that motivates you, embrace it.
When the interviewer ask questions about motivation, the interviewer wants to know:
Why you want to work with them
The reason or reasons why you choose their organization
What you know about them
Whether or not you are the right fit for the company and the job
Whether or not you are really ready to work for them
Whether you understand the job you are applying for
Why you are interested in the position for which you are applying
If you can handle the responsibilities associated with the job
If you have the right qualifications for the job
If the job matches your personality
If you are coming for the money, not for the company
What gets you going? What gets you up in the morning?
This is not a complete list. If you want to ACE motivation questions, study everything you know about motivation. You can do it!