How to come up with an effective undergraduate research topic - for scholarship?
Generally speaking, developing a research topic is something that happens over weeks, months, even years - it's not really something that naturally comes about in a single day. So reasonably speaking, you really need an alternate question: how to come up with something reasonable to put in a scholarship form in a few hours. The usual process is to talk with lots of professors and potential advisers, read over their research, look carefully at all topics that come up in class, read a variety of books and keep your mind open and working on what you are really interested in...and that is going to take a lot more time than you have.

So frankly, you are going to need to "wing it" - to "fire from the hip" and hope for the best in terms of this particular scholarship application if it indeed has the hard deadline of 'today'. For this I would suggest you review the general ideas in this helpful professor's published works, as you mentioned you have already done, and point your finger towards whatever topic sounds kind of doable to you and is generally an area you might like to work more on in the future - or at least you think you might like to. And something vaguely in that realm could be your proposed topic. Just write it up and get it out.

Once you have gotten past the emergency of the deadline, you should certainly talk with the professor more about potential topics. But there is no replacement for having your own ideas and interests, and what is a great topic for one person is torture to someone else. By all means, keep working on it and developing your interests and awareness of what you might like to work on in the future - but for now, get that scholarship app done while you still can!