You don't need to know about the other candidates specifically to answer these questions. You need to know about yourself. There are essentially three kinds of answers to these questions:
- meta talk like refusing to answer, claiming you don't know the other candidates, declaring that finding this out is the interviewers job
- claiming an attribute that clearly everyone has - I can speak English during an interview process that is taking place in English, or I can read and write for an office job, or that are irrelevant to the job - I know my way around the city where I live very well
- claiming an attribute that is relevant to the job and that not all candidates are guaranteed to have. Only this one helps you get the job. Figure out what it is.
So, if you're applying to work in an office, claiming to be a team player, to work well under pressure, to know the particular skill they are hiring for (eg a specific programming language, a specific piece of software everyone in the field uses), to be punctual - these are useless answers. Everyone can do that.
But if you are certified in the skill, and you know only about a quarter of people in your field are certified, that's an interesting thing to point out. If you have won awards, or spoken at conferences, or love to lead lunch-and-learn sessions for your coworkers, that sets you apart. If you have already led a team through the transition your future employer is about to start, if you've been using that technology dramatically longer than most people (you were a VERY early adopter) or have some other insider connection such as working at the place it was developed and using it while it was under development, these are things that set you apart.
While it's easy to claim this is a lazy question, it can still be powerfully useful. If I was handed a sheet of paper and told to ask candidates this, I could screen out all the ones who claimed irrelevant skills (like a pilots license for a software developer - and yes, that might be relevant, it would be up to you to show me that in your answer) or non-differentiating skills like "able to use Excel and Word as required". And a candidate who knows that their speaking, teaching, leading, project-managing, planning, scripting, build-configuring, or negotiating skills are far above their peers and would really help this project can tell me so directly, which is helpful. I will probably ask more questions and drill in on those claims, but to have them handed to me by just asking is quicker than me eventually noticing a common thread in the stories of success the candidate has been telling me.
People sometimes worry that if they say "well, I love public speaking and would be happy to represent the team at presentations or conferences" that the interviewer will think "what a moron! We had someone yesterday who loved public speaking. This candidate clearly knows nothing about the other candidates. I'm going no-hire on this one." That's only a risk if you claim to be able to breathe air or sign on to your laptop. It's actually a super softball question that doesn't require knowing much about your competition other than a vague awareness of the mandatory skills they all must have. It really is a question about you -- answer it.