As regards Norse and Finnish mythology, and even as regards the medieval or medievalist Arthurian materials, I'm doubtful about the required reading. For example, when Lewis writes about reading Malory, as I recall, it sounds like his own discovery, thanks to the Everyman's Library books. My guess is that Lewis and Tolkien might have encountered Arthurian materials in two forms as assigned reading: early on, maybe some kind of retelling of the Round Table etc in a school textbook written by someone no one remembers now, and later in Tennyson's
Idylls (selections), etc. But I'm just guessing. Likewise, I'd guess they got some Classical mythology in retellings early on, and later encountered some in the form of glosses on Shakespeare, etc., but I'm doubtful that they would have had more than incidental encounters with Scandinavian mythology through their curricula. Here too Lewis's letters and autobiography indicate that he must have known little or nothing about Siegfried and the dragon till he saw an article in a magazine for gramophone fans! The article had one or reproductions (monochrome, I assume) of Arthur Rackham art for Wagner -- but the article and art got Lewis going. I'd have to check, but my sense is that he started writing a poem or drama about Siegfried with little or nothing to go on but the magazine article.
View attachment 48835
Hugh, if you've read
Surprised by Joy, you'll probably remember some of this. For Tolkien -- he discovered the Siegfried/Sigurd story in one of Andrew Lang's "color" fairy-tales books. I don't think it was assigned reading, though it might have been a school library book. (I wonder if someone could compile an interesting anthology of such things -- young people who became fantasy writers discovering some great things in school libraries and public libraries.)