How to access CoreData model in today extension (iOS)

What you really want is to access your persistent store (most likely a SQLite database). In order to achieve that, you need to configure App Groups and make sure that your host app configures the Core Data stack using your shared container (so your store is accessible in extension as well). Something like:

    NSString *containerPath = [[NSFileManager defaultManager] containerURLForSecurityApplicationGroupIdentifier:YOUR_SECURITY_APP_GROUP].path;
    NSString *sqlitePath = [NSString stringWithFormat:@"%@/%@", containerPath, @"database.sqlite"];

Then in your extension just create persistent store coordinator with managed object contexts using database in shared container. You can share your model (.momd) and managed object subclasses with extension just by making sure they are included in extension target as well.

Edit:

To add your model and managed object subclasses:

1. Make sure you have your app and extension targets

   

2. Click on your model file, and select both targets under 'Target Membership' on right-hand panel

   

3. Repeat the same with all your managed object subclasses