This question is a bit too short to answer unambiguously. It most likely refers to Will Byers getting powers in Stranger Things, but “what episode” could apply to several different series or characters.
Clarifying the character
The best‑known “Will” who recently “gets powers” is Will Byers in Stranger Things season 5. In that storyline, Will first visibly manifests and actively uses his powers in season 5, episode 4.
If you meant a different character named Will (for example, from another show, anime, or cartoon), specifying the series (and season, if you know it) will make it possible to give an exact episode number.