I am using K2 on my site and am completely lost when it comes to how to assign an item title (headline), publish up date, article intro text, article body text, description, and image to their respective properties for structured data.
During installation I went into the "Overrides" tab and copied the K2 from the left-hand column. My question is, do I still have to change code manually in a page to get this all to work correctly? If so, for K2, where is this done.
J4Schema allows you to create tokens and inject them inside your HTML code whereever you want, not just inside articles as in the free version.
Since it's not so easy to find the right spot where you can add microdata, inside the PRO version we ship some template overrides, so you can copy them and use them immediatly (this is what we did for our test site).
Now, to your question.
After copying J4Schema template overrides, your site will automatically have microdata in the right place. If you want to test that, you can take a look at the HTML code and search for "itemprop".
Moreover, inside the PRO version you have a module that will generate a link that will let you check your current page vs google rich snippets tester.