I got it working with BlueprintImplementableEvent. But what I really want is a BlueprintNativeEvent.
I did just as you said for the BlueprintNativeEvent (I copied the code over) and I get following error:
Error 2 error LNK2001: unresolved external symbol “public: virtual void __cdecl AUltimateTutorialsCharacter::TakeDmg_Implementation(int)” (?TakeDmg_Implementation@AUltimateTutorialsCharacter@@UEAAXH@Z) E:\GitHub\UE4—UltimateTutorialMap\UltimateTutorials\Intermediate\ProjectFiles\UltimateTutorialsCharacter.cpp.obj UltimateTutorials
My whole Project is on Github. So if you want to take a look.
/tree/experimental
I just pushed the latest files to Experimental Branch 