I used the Visual Studio 2017 (ASP.NET Core 2.0) SPA Aurelia template to create a new solution, but I am missing the aurelia.json file. Why doesn't it get created? It is also not clear where the "resources" folder has to be created.
The aurelia.json file does not get created because it is needed by the Aurelia CLI build tool only. Since the VS template uses Webpack as a build tool, aurelia.json is unnecessary - you configure your build process by tweaking the Webpack configuration files.
About the resources folder, I guess that you refer to the one that is created by the Aurelia CLI au new command, that is, the one in which you generally store your reusable components and similar things. If that is the case, technically, it shouldn't matter where it is as long as you properly configure your imports, such as .feature('resources'), in your main.ts (or boot.ts as it is called when created by the VS template) - though for the sake of making it easy to oversee your project structure, I suggest you sticking to the structure that is created by the au new CLI command, and create your resources folder directly inside the ClientApp folder.