What could be the best possible way to have a trading mentor?
There is no "the best possible way". There is only luck. If you are lucky enough to have an experienced trader among your relatives or friends, then this is the only way to get a mentor.could it be to select a mentor and then let them know that you have chosen them as your mentor
Yeah, give him an honorary mentor badge to boot. 
The mentor himself should tell you that he is ready to teach you. But I don't think that strangers will want to waste their time teaching a competitor for themselves. Even for a fee. I believe that only a close person can become a mentor, in some sense a trading partner, who will benefit from teaching you as an assistant, for example. But for this, "all the stars must align".
or follow them anonymously without their knowledge that their mentoring someone, and you are following in their steps?
Whats your thought?
Oh, yeah. Start stalking him. Whats your thought?
I think you should get rid of the illusion that some mystical trader will show up and teach you all the secrets of trading, after which you will become fabulously rich. You are looking for an easy way. It doesn't happen. There is one effective way, it is to study and gain experience. Otherwise, it is impossible to achieve success in any business. Including trading.