What is the best plugin for 8D surround sound editing in audacity?
“8D sound” is a pseudo-scientific name that someone made up for sound that pans around a lot. (See: https://www.quora.com/Whats-the-difference-between-3D-8D-and-16D-sound).
There are a number of panning effects for Audacity available on the Audacity wiki: https://wiki.audacityteam.org/wiki/Nyquist_Effect_Plug-ins#Amplify.2C_Mix_and_Pan_Effects
There are probably also VST panning effects that will work in Audacity (but I don’t use VST effects).