The interviewer wants to see that you are forward-thinking and have identified challenges in your industry in the next few years. As this question asks your opinion, there is no wrong answer. However, if you have no response to what challenges you will face as a dementia care specialist, the interviewers will determine that you haven't put much thought into the future. It is also recommended to ask the interviewer what they think the most significant challenges will be. It shows you are interested in hearing what they have to say and value their experience.