Dưới đây là các câu hoàn chỉnh theo yêu cầu:

1. **Why do you want to have this job in the future?**
- I have always wanted to become a doctor / dreamed of becoming a successful engineer.

2. **What benefits can you get when you have this job?**
- If I am successful in my job, I will have the opportunity to help many people and earn a stable income.

3. **What should you do to prepare for it?**
- I will/am going to enroll in a relevant degree program and gain practical experience through internships.