Before answering, I'd like to again remind you that we're talking about a world where the concept of intellectual property does not exist.

> your primary activity can only be remunerated via donations

I don't think the word "donations" really applies here, just like tips at a restaurant are not considered donations. Tips are not legally required, but they are heavily socially encouraged. If everyone agrees that creative works and knowledge should be shared and that we want more of them to exist, then it is expected, though not required that you give something back. Ideally proportional to the use you got out of it and what you have in the first place.

> On top of that, each one of those people may decide to publish your book as their own.

They can share the book all they want, but that doesn't mean they get to lie about who made the book ("as their own"), that should probably be illegal ;)

> But, continuing the hypothetical, why would you do that? Why would you spend the effort to compile all your knowledge in book form?

Maybe I hope to get compensated for it, maybe I like writing books, maybe I wrote the book for my own use and decided to share, maybe I personally value getting this knowledge out there for others to use which may even benefit me, maybe I feel grateful for the knowledge I received for free myself and want to give soemething back or build upon it or maybe I'm just obssessed with books :)

> Typesetting is hard, and you may want to use the expertise of other people for editorial review, printing and binding. Everything you pay them will be out of your own pocket, since the expected market value of the finished product is zero.

Probably if I only know about writing the book, it would make more sense to release a PDF, and maybe someone else will want to go through the trouble of actually making it into a printable book for some portion of the tips. Maybe they'd like to cooperate with me on the "official" release of the book for some share of the tips, after all anyone could possibly piggyback on their derivative work (or just get the PDF :)) so they may get more out of it by being part of the "original" "official" version of my book. Or maybe I can just pay them if it seems valuable to me.

> and may have to if they want to recoup their own costs

Or as above, they'll find it easier to recoup their costs by cooperating ;)

> Taking a slightly wider view, how are you going to convince the bank to lend you a mortgage if your primary activity can only be remunerated via donations?

As in our existing world, if the bank thinks I'll get enough back in tips, then it is a worthwhile investment. Also, in our hypothetical world, since everything is already available "for free", the best place to spend your budget for creative work is in works that don't already exist, making crowdsourcing a much more popular and rewarding option (I can get Eat Pray Love for free, but adverblessly's book is priceless since it will only exist if they get this money).

> In this world, who would still spend time on publishing books?

If we're talking about online publishing, I'm sure you could find plenty of people that will setup a website to host PDFs (or epub or mobi :)) for a 10% comission, guaranteeing the original artist gets at least 85% of the sale price (if it isn't going to the original artist, why even pay?). If w'ere talking about physical book publishing we'd probably see a similar dynamic. Alternatively, maybe you'll get your PDF from the original artist to tip them and then go to the professional printer for the physical book at printing cost +10% profit margin (at whichever book printer provides the best cost/quality for your needs).