From Ng et al.:

Political knowledge and skills included the following two measures: political knowledge (e.g., Chao, O’Leary-Kelly, Wolf, Klein, & Gardner, 1994; Seibert, Kraimer, & Crant, 2001) and supervisor-focused political tactics (e.g., Wayne, Liden, Graf, & Ferris, 1997)

Taking the Chao paper as an example, they look at things like "do you know who the most influential people in your organization are?" and "do you know what to do to get the most desirable work assignments?"

The Wayne paper looked at how frequently people used the tactics I listed in the article.