If the other book was created using iBooks Author, you can link to a specific location in it using the same link structure as above, but include the asset ID in the link. For example:
ibooks://assetid/496292471#page(10)
ibooks://assetid/496292471#chapter(2)
To find a book’s asset ID, control-click (or right-click on Windows) the book on Apple Books and copy the link. In the example below, the asset ID is 496292471:
https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewMetaBook?cc=us&id=496292471&mt=13