Google has a site verification process outlined here:

The "Upload an HTML file" option will not work with Luminate Online due to the way that the system handles page not found problems. As such you will need to add the meta tag that Google will provide instead. The easiest way to do this is:
  1. Select Setup > PageWrapper Editor
  2. Click Edit next to your PageWrapper
  3. Go to step 2. Meta Tags
  4. Find the section labeled "Additional HTML Tags for HEAD Element" and insert the meta tag
  5. Click Save

The meta tag should look something like this, and will be unique to each request for verification, so be sure to get your tag from Google's site:
<meta name="verify-v1" content="kz0IN0OUqfEYRpyZI5LoFvshnRUz8yB1T35lbuc6jw4=" />

If you have multiple PageWrappers, this process will need to be followed for each of the PageWrappers.  You may also consider putting the meta tag into a reusable PageBuilder page and inserting this reusable Page Builder page into the PageWrapper's meta tags instead of directly inserting the meta tag itself. This technique will allow you to more easily correct and/or update the meta tag when needed.