I get this question a lot from mistresses i've talked with, and honestly, I can't trace my interest in femdom back to a single point.

I know when I watched cartoons as a kid I always loved it when the villainesses would win (Even if that victory rarely lasted) and when I played videogames I remember purposefully losing to female enemies.
Specifically as a kid I would play my older brother's copy of Soul Caliber 2 on Dreamcast (Despite my parents telling him to never let me play it because of the violence) and in that game there's literally a dominatrix themed character wielding a whip, if she knocked you on the ground I vividly remember one of her moves was to step on you with her heels and when she won she would always say something insulting, even as a little kid with next to no sexual desires I always liked losing to her on purpose.
So that's probably one of the origins of my masochism and kink for corporal punishment!

Thinking about it a little harder, I remember the origin for my facesitting fetish now!
When I was in middle school I remember watching the WWE divas and every once in awhile they would do this move call the "stinkface" where they would have their opponent sitting down in the corner of the ring, both arms on the ropes, and then they would get some distance before running back and slamming their ass on the opponent's face and rubbing it in!
Watching videos of that I always felt like I was watching something I shouldn't be, I hadn't watched porn before then, but I think that kind of acted as my safe-for-work gateway drug into porn and more specifically femdom porn. It definitely activated my kink of forced facesitting and ass smothering for sure.