I've always wondered of there ever was or is, a TES equivalent of a Witcher from Andrzej Sapkowski's Witcher series?

Is there?

Haven't played the games but as far as I can tell there are two things that make a person a Witcher: body modification and hunting monsters.

1. Lots of folks hunt monsters in TES. Join the fighters guild.

2. Forsworn Briarhearts. They have their heart removed and replaced with a Briarheart. This gives them enhanced magical and combat abilities as well as extremely good hearing, beyond normal human levels.

They also have a bit of that native wildfolk thing going on.