How to output to console in UWP on Windows 10?
You can use Debug.WriteLine method from System.Diagnostics namespace
MSDN Link
When you start debugging your application those messages will be displayed in the Output Window (Standard VS shortcut is Ctrl+Alt+O, ReSharper shortcut is Ctrl+W, O)
Starting with RS4 (the release coming out mid-2018) you can build command - line apps with UWP or output info to the command line. The pre-release SDK is already available and you can watch a Channel 9 video.