I'm using a Content Query web part in SharePoint 2013 in O365. I want to include all items from the root site and all subsites except one particular subsite.
In the CQWP, I can only select items from the site collection, from a site and all it's subsites or from a list.
Is there a way to do this?
My answer is "No", as you can see, we can't find such settings in the tool pane of this web part, which indicates that it is not supported by design.
Content search web part(aka CSWP), it should enable you write some complex queries with KQL to search the data you want(exclude from a site or a library), just give it a try.
A sample query text which is set in the CSWP, it will exclude the results from a specific site: http://i.stack.imgur.com/FIOPD.png