I explored a little, and figured out that coordinates are in the form: X Y and Z. So I decided to use:
GetActor()->GetActorLocation().X, GetActor()->GetActorLocation().Y, GetActor()->GetActorLocation().Z;
in the UE_LOG macro with the %f specifier 
There is only a problem. if you want to GetOwner()->GetActorLocation().X.ToString() it wont work
but GetOwner()->GetActorLocation().ToString() works. i dont know why.
You are using %f which is fine, but what if you have a FString pos = GetOwner()->GetActorLocation().X ?, i got this problem.