The hiring authority is looking to see that you have a full understanding of your responsibilities as a recruiter. By discussing what you believe to be the top 3 activities you will be doing in this role, you are showing the interviewer that you have an understanding of the job.
If you are currently working as a recruiter, discuss what you now take care of in your role, on a daily or weekly basis. If you are new to the recruitment world, lean on what you know from research and the job description or job posting.
"The top three most important activities as a recruiter are to develop a solid candidate pool, created trusting client relationships, and dive into business development. These three tasks will ensure that I have a strong amount of job orders, enough candidates to quickly fill my positions, and a great reputation to build on."
"From what I have read in the job posting, it's important that I spend a lot of time interviewing candidates, performing a variety of business development activities, and following up with my candidates. Documentation is also an important function, ensuring that my accounts remain up to date at all times."