You can't. Major publishers publish thousands of books a year that don't sell. Movie studios release hundreds of movies that no one watches. TV Networks create new shows every season that get cancelled after a few episodes because no one watches. We don't know how to evaluate if a book will sell or not.
I once asked my publisher if the sales for one of my books was in line with his expectations. (It is a niche book.) He said he has given up forming expectations about how books will sell. He just can't tell.
You can, of course, tell that an awful lot of manuscripts and book proposals won't sell because they are obvious drek. But there is also the category of not-drek-but-not-currently-fashionable stuff that is often rejected many times before it is finally published and sells millions. (Harry Potter is the current go to example of this, but there are many others.)
What you can do is try to build an audience for a book. For the book I mentioned above I wrote a blog for 18 months before I even pitched the book. The blog built an audience, which in turn helped sell the publisher on the book and now continues to help the book sell.
For non-fiction, any publisher is going to ask you two basic questions. 1) Why are you the best person to write this book? 2) Do you have an audience? If you don't have good answers to those things, they are not going to read your chapter. If you have a good answer to the second question, the first takes care of itself.
So, work on building an audience. That will probably take longer than a few weeks, but the interaction you get from your audience will make it a much better book.