What search skill has Nino not mastered if his search results for "rain*" include unrelated topics?

The focus here is on Nino's ability to refine his search results effectively. When using the term "rain*" with the asterisk, Nino is employing truncation, which is a technique that allows for the inclusion of various word endings. This means that it should capture terms like "rain," "raining," and "rainy." If his search results include unrelated topics, it indicates that he is not using keyword specificity adequately. Keyword specificity requires selecting precise terms that clearly define the desired information, thereby reducing irrelevant results.

Truncation itself, indicated by the use of the asterisk, is being utilized, which means Nino has mastered that particular skill, but the unrelated nature of the results suggests that the underlying issue lies in how specific his keywords are in relation to the topic he is researching. Therefore, the skill that Nino has not mastered is the ability to be specific with his keywords to effectively narrow down the search results to relevant content.