You might have caught what Agnarr said when you first saw Frozen II, and if you knew that Frozen was based on Hans Christian Andersen's The Snow Queen from back when the first movie came out, then you likely knew exactly what was being referred to here, as he's the Danish author in question. However, if you were paying too close attention to what was being said, you might have missed what was being shown. The book Agnarr is reading isn't The Snow Queen, but actually one of the author's other stories that was turned into an animated Disney musical, The Little Mermaid. The logo seen here is specific to the Disney movie version.