It's good to have some basic knowledge about networking before starting to learn about WebRTC.
Basic knowledge about IP addresses & Ports (Sockets) and about P2P networks
should be enough. And yes, knowledge about JavaScript is important to code WebRTC based web applications and some knowledge about NodeJS or other server side languages if you want to implement a signalling server for the WebRTC application or you could just use some code in GitHub.
But it's fine, you can still learn WebRTC with some abstraction, it's just that you might get confused with what's going on
or might wanna know the subject in a more better manner to wrap your head around it.