I have picked up a Mackie analog mixer. I want to know where it’s possible to have one of the audio events (tracks) in my Cubase 8 AI routed out to the analog mixer so I can add some compression or other effect and have it come back inside the DAW. I am just experimenting and want to add some outboard effects to certain individual tracks (audio events) and then A/B it with and without the outboard effects? is this possible? And if so, how do I route my interface/computer to my analog mixer?
Yes you can, as I already wrote in your other thread. 
Of course depending on your interface.Without posting any useful info on what audio interface it will get difficult to get useful answers
Audio interface is ESU1808