This is a question probably better posed to Ginger Labs, the developer of Notability. As you already know, Notability is an iOS-only app and there is (currently) no Mac version.
That said, you do have the ability to export notes and save them to a variety of places, including Dropbox, Google Drive, and any WebDAV server. There they can be opened by compatible apps on your Macbook. The export allows you to select what gets exported including the PDF, Paper, and the audio recordings associated with a note.
Just understand that you have to do this individually for each note, and if you change your notes, they will not be synced back and forth.
Unfortunately, and as stated by Notability's support site, the iCloud feature is only meant to sync the notes between iOS devices. There's no real storage on iCloud of the notes that you can access.
You can however turn on the Auto-Backup feature, and have a copy of the notes be stored on a Cloud service such as Dropbox or Google Drive automatically, which you can then access from your MacBook through a browser, or their own Apps.