Can I watch CNN live in Apple TV?

Yes, but you may need to have a TV provider subscription already to access it. (“10 minute preview each day, log in with your satellite or cable provider for unlimited viewing.”)

It may also depend on your country or region, as it is not the same everywhere. (“Video on Demand and Live TV limited to US consumers.”)

CNN app - App Store Preview - Apple (US)

Yes but you need a tv provider to view for longer. There’s other apps like ABC 7 news that has live content without signing in. NBC News requires living in the US.

Some YouTube channels have live news as well.