In recent years, there has been widespread concern about misinformation and hateful content on social media that are damaging societies. Being one of the most influential social media that practically serves as a newsearch engine, YouTube has accepted criticisms of being a major conduit of misinformation. However, it is often neglected that there exist communities on YouTube that aim to produce credible and informative content - usually falling under the educational category. One way to characterize this valuable content is to find references entailed to each video. While such citation practices function as a voluntary gatekeeping culture within the community, how they are actually done varies and remains unquestioned. Our study aims to investigate common citation practices in major knowledge communication channels on YouTube. After investigating 44 videos manually sampled from YouTube, we characterized two common referencing methods, namely bibliographies and in-video citations. We then selected 129 referenced resources, assessed and categorized their availability as being immediate, conditional, and absent. After relating the observed referencing methods to the characteristics of the knowledge communication community, we show that the usability of references could vary depending on viewers' user profiles. Furthermore, we witnessed the use of rich-text technologies that can enrich the usability of online video resources. Finally, we discuss design implications for the platform to have a standardized referencing convention that can promote information credibility and improve user experience, especially valuable for the young audiences who tend to watch this content.