Not sure you should be moved, as this seems like a legitimate agent question to me. If you're not getting responses to your post, it may just be that no one (so far) feels they can offer up a good or informative enough answer. Many of us on here are fiction writers (like me) and perhaps not that familiar with how nonfiction book proposals work. I do know that by asking about your platform, the agent wants to know if you already have a built-in (established) audience for your work. Having an active website, for example, is usually a big plus. Exposure on TV and radio, or having a regular newspaper column with a readership, are also big pluses. In other words, they want to know there are people who are going to read this book once it's out there. This idea of having a platform is usually much more desired for nonfiction than fiction (though not really sure why).
Hopefully someone else with a bit more non-fiction experience can offer up more advice for you.