I’m having trouble deciding which game I want to start speedrunning. Most games i like ( such as Skyrim) are better to speedrun on pc. But i only have an Xbox one. I would appreciate if anyone could help me to find something.

Everything that is on Xbox One is on PC, with the literal sole exception of Rare Replay (and even then, most of those games can probably emulated). If Xbox One is your only platform, don't worry about being super duper optimal. Just find a game you like and play it as fast as you can. Doesn't need to be any more complicated than that. You will need to have video proof of your runs, so either stream to twitch or Mixer (enable VOD saving if you do) or use a camera to record your TV screen.

Perfect Dark Zero! It's an Xbox only FPS, on 360 but is backwards compatible on xb1