I'm planning to read it very soon. The Magic Mountain is, in my opinion, a masterpiece ranking among the greatest novels I've ever read. I'm a fan of long, dense novels, and Joseph and his Brothers is by all accounts his most dense and rewarding novel.
I haven’t read it, though I intend to. I would be surprised if the book required much knowledge of the Bible considering the story of Joseph is contained in Genesis alone, and possibly somewhere in the Quran, but I’m not certain Mann draws from that work. I think I would be much more concerned with brushing up on the Amarna period in Egyptian history because that’s apparently where Mann sets the story. I am not familiar with Egyptian history, so I will have my work cut out for me when I end up reading this.
Zero biblical knowledge *required*, but personally I would recommend at least reading the book of Genesis beforehand if you haven't.
Joseph and His Brothers is a masterpiece in my opinion though, I stopped reading The Magic Mountain at page 89, it just wasn't gripping me, and have yet to return to it, but JaHB sucked me in from page 1 and didn't let go.
I read it; is it good? Yes, having read all of Manns books I'd personally consider it his magnus opum. Do you need biblical foreknowledge? Dont know if it's mandatory but having read the bible/old testament will defentley enhance your reading experience (at least read the Joseph story if you dont want to read the bible, which btw you should do anyways sooner or later, religious or not, it's prolly the most influential/referenced text ever, and it's genuienly a decent book, and you can skip the non-narrative parts. Also consider reading the Epic of Gilgamesh, since it's also referenced quite a bit)
I read it many years ago It is the first of a tetralogy. I found it fascinating and I really don't believe you need any special knowledge of the Bible to enjoy it. Mann has always been one of my favorite authors.