Like IQ, one's NFC is primarily judged by psychometric self-evaluation rather than behavior. The way in which we recognize NFC from a behavioral standpoint is to recognize the ways in which they seem to produce behaviors that a NFC psychometric test would evaluate.
In other words, if you want to recognize high NFC in others, you might want to familiarize yourself with the questions and traits that psychometric tests associate with high NFC. For example, this test asks questions that are representative of high NFC. So if you were to recognize someone who might answer 'yes' to "I usually end up deliberating about issues even when they do not affect me personally", or "I find satisfaction in deliberating hard and for long hours", then you could most likely recognize someone with high NFC.
Other behaviors may be less subtle. For example:
[Those with high need for cognition] like to engage in complex, inquisitive, and analytical thoughts. They feel intrinsically motivated to devote effort to cognitive endeavors, striving to understand objects, events, and individuals. These individuals are less inclined to be biased by superficial factors, such as the appearance of speakers or social comparisons. In addition, they are more inclined to enjoy some experience if their expectations were low.
Interestingly, both need for cognition, as well as need for affect--the motivation to experience strong emotions--increase the likelihood that people will become transported into these narratives (Thompson & Haddock, 2012). If need for cognition is elevated, people contemplate the tales more extensively, and appreciate the complexity of narratives, both of which facilitate transportation. If need for affect is elevated, people enjoy the emotions that transportation can evoke. The implication of this possibility is that need for cognition can, in some instances, increase the susceptibility of people to messages. For example, if an advertisement presents a narrative, need for cognition can facilitate transportation and thus diminish the likelihood of counterarguments. In contrast, if an advertisement presents a series of facts, instead of a narrative, transportation is precluded, and need for cognition could increase the likelihood of counterarguments.
Insofar as NFC and extraversion is concerned, there appears to be a positive correlation between need for cognition, openness, and conscientiousness. Thus, it is represented by openness to new and novel ideas and a willingness to engage in effortful thought (Verplanken, Hazenberg, & Palenewen, 1992). It does not appear to be linked to extroversion.