I'm trying to play TCS on PC but every time I try to start the game I cant see live split. What do I do?

If you go to layout > layout settngs there should be an "Always on top" button near the bottom of the tab

Since TCS is always in full screen, you can't get livesplit to show over the game. Most runners put livesplit on their second monitor. If you only have one monitor you can screenshare livesplit on discord and watch on your phone or another device.

I would recommend what Lazer said as a solution, but some other possible workarounds include streaming to Twitch and watching the stream on another device, playing in forced windowed via a third party tool such as dxwnd (this will make a few tricks in the game impossible, I personally would not recommend this), or hooking up your PC to a second monitor or even a television to be able to see them.