Starting a project in Xcode 10 doesn't present the checkbox found in previous versions of Xcode. How do I include CoreData in my project?
Nothing has changed in this regard. The Core Data option is present in exactly the same places as in previous versions of Xcode. You have to start your iOS app project with the Single View or Master-Detail app template.
If you're starting from a different app template, just copy the desired code from a project started with one of those templates.