I believe there's another post around here where Jeremy explains that if you're using the release version of Jounce (e.g. from NuGet) you won't see any output because the default logger uses Debug.WriteLine and but Debug.WriteLine is marked with a Conditional
attribute so it doesn't execute in a release assembly.
I was struggling with the same thing until I found that explanation, which made perfect sense. At that point I just pulled in the source for the Jounce DefaultLogger and marked it with [Export(typeof(ILogger))] and all was good :-)