0 knowledge on ANYTHING, square 1 basically. Where can someone start and lead into the general direction to start off a career in this profession.
I think it depends on what you want as an outcome. If you're starting from scratch in terms of security, I would recommend placing ethical hacking on the backburner while you gain some foundations around security with a focus on network and application security concepts. If you are looking to research or pentest a particular product or system, consider diving deep on areas related to that particular technology/technologies.
The main thing to remember is that ethical hacking is always an application of security against a system. So knowing how security works is really important!
You can initiate by taking a course such as CEH (Certified Ethical Hacker). This will provide you with the foundation and gives you an overall knowledge of hacking. Alternatively, if you do not wish to spend money on this course then you can learn yourself. But learning by yourself might be difficult and you might get lost as there is a range of topics to choose from. Anyway, you can start self-learning from sites like cybrary. There are enough videos on the site where you can explore the field of Information Security. Lastly, consistency is the key, learn a new thing each day and you will become an expert in no time.