Yes, you can use pubsub, there are some endpoints listed in the docs https://dev.twitch.tv/docs/extensions/reference
There are limitations to it though, for example it’s designed as a way for your backend to send data to either all extension users (globally), all users on a specific channel (broadcast), or to a single user (whisper). Users can listen to pubsub, but can’t send messages, although the broadcaster does have some limited pubsub sending capability within their own channel.
So if you need users to send anything to your EBS, it can’t be done over pubsub.