Assets file '<path>\project.assets.json' not found. Run a NuGet package restore to generate this file.

or

C:\Program Files\dotnet\sdk\2.1.504\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(198, 5): error NETSDK1004: 找不到资产文件 project.assets.json

Solution:

Use cmd cd in  .net core project files
Run dotnet build