See if the user is question has correct email address within PPM. Wrong email address could cause email to not reach the intended person. If above is not the case, then use the same token in the email body and send that email to yourself thru the same workflow. You can verify the value that the token resolves to.
In either cases you will have the notification history table to look at to see if any entries were made. If not then your notification is not getting triggered at all.