I would argue that this depends on the network topology.
In a switched network, where every device is attached to a port on a switch via lan cable, the switch transports the ethernet frames only to the destination port. every other port with an attached device can not see the frames. So in a (not compromised!) switched network, nobody can read your data except the receiver.
However if every device resides in the same collision domain, for example a wifi network, then technically every device can read every frame beeing sent. Ordinary network cards refuse frames which are not adressed to their mac-address, but some network cards can be configured to listen to everything (this is called promiscuous mode). A hacker usually uses such a network card.
So, when a hacker can read your frames, the question is whats the content inside the frames. Unencrypted traffic such as http, ftp, ... can be read without a problem. So, as the other comments say, check if all your traffic uses encrypted protocols like https.
BUT to be clear, attacking a wifi network (especially when you already have access to it) isn't a big thing and there is a wide range of attacks for this exact scenario. So I would say, in a wifi network which is not controlled by your or where you don't know every member of the network, you are never 100% safe. However using https is the most important thing you can do to keep your content private.