You cannot search another member's Bookshelf, but you can browse it. You can re-sort the member's Bookshelf using any of our 6 sort options and you can choose just to view the indexed books. If you want to know whether a member owns a specific book, you would click the Bookshelves icon for that particular book and look for their username. It helps if you know the size of their Bookshelf since the list is sorted by that.