You can’t create a Siri Shortcut that includes a variable, for example “Add TitleOfBook to reading list”.
But there is a workaround for it, using the Shortcut App. There is a Dictation-command and you can use the result as a variable in following commands.
I’ve done that with Things 3:
Command 1: Dictate Text (I don’t know if it’s the correct naming in English, I’m using German) --> Book Title
Command 2: Dictate Text --> Author
Command 3: “Add Things To Do” with the following parameters:
Title: Dictated Text (the shortcut-App shows this variable on top of the keyboard, so click on it)
Liste: Lesen (the name of the reading list in Things 3)
Notes Field: Dictated Text (the shortcut-App shows this variable on top of the keyboard, so click on it)
How to use:
“Hey Siri, add to list reading” (you have to tell Siri to use “add to list reading” as command for this workflow)
Wait for Dication Window, then dictate the title of the Book.
Wait for Dictation Window, then dictate the name of the author.
It’s far away from being optimal. Normally you would say “Add TitleOfBook from TheAuthor to list reading”, but it’s the best approach for now, I think.