There are two ways. When you finish your wix and hit publish. Once it finished saving there will be a box that pops up. In the bottom left corner of that box there is a button that says this (> Embed) click that. The code that appears in the box labeled your code is your embeded code.
If it doesn't work another way to grab the code is to go to your active wix.com site and grab it.
This is where it is on your active site.Hope that helps! ^_^