What do you call a contraption for holding newspapers?

It is a newspaper holding stick

Newspaper holder generally refers to different kind of container where you keep papers and magazines.

It appears this is closely if not inseparably linked to Vienna and Viennese coffeehouses.

Hammacher Schlemmer sells them as Viennese Coffeehouse Newspaper Holders. Zangra also calls them Newspaper Holders and links them directly to Viennese coffehouses.

The travel site Vienna Unwrapped lists them as one of their top five insider gifts to buy in Vienna.

So I think the best you can do is newspaper holder and if you want to explicitly refer to the type shown in your question, go with Viennese coffeehouse newspaper holder.

As a native of Vienna I'd use Viennese newspaper holder (a) which is the literal translation of the German term Wiener Zeitungshalter. Other devices which are not as sophisticated I'd call newspaper sticks (b).