Hi Diego
Here's 5 versions. Each has a different meaning or emphasis, depending on where you place the word 'really':
"nobody knows who I am, really" = to be honest, nobody knows who I am
"nobody knows who I really am" = nobody knows the real person that is me
"nobody really knows who I am" = nobody has a great depth of knowledge about who I am
"really, noboody knows who I am" = in reality, nobody knows who I am
"Really! Nobody knows who I am" = oh for goodness sake, nobody knows who I am