Does anybody know what this tool is called?

It's a pair of canvas pliers. They're used to stretch canvas over braces, used in painting prep.

Answer source: Matt Velic, data professional and noted art graduate.

Specifically, it appears to be a Fredrix Canvas Pliers #7400 tool.
Here's a link to the manufacturers page (scroll to the bottom) Fredrix Canvas Pliers tool manufacturer:

and a vendor page with a picture that more closely matches the book cover, Fredrix Canvas Pliers tool for sale. It looks like the spring has been removed from the tool on the book cover:

It almost looks like a sheet metal seeming tool.