Specialized knowledge is usually new knowledge which has been discovered by one or only a few identifiable people. This knowledge may or may not have been published, but it is the intellectual property of the person who has discovered it. If you use such knowledge in your own work, you MUST acknowledge the source of your information unless you are the person who made the original discovery. You are, however, as college students, in the peculiar position of having too little experience in most fields to know whether something which has been published is commonly known or not. Be safe and acknowledge any idea or opinion or fact you take from any source except dictionaries, encyclopedias, almanacs, or news stories from reputable newspapers and magazines.
Opinions are always specialized knowledge.
Even your own opinions, if published, become your property, though inexpert opinions have little value and are seldom original enough to be claimed as property. If you use an opinion which you have received from a published source, you must acknowledge the source. This not only respects the property rights of the author and publisher, it protects YOU as well. If your conclusions are based on his work and you modestly acknowledge your source, then people have little reason to believe you are a bad thinker yourself. Of course, the most important reason you should acknowledge sources of specialized knowledge is that when you do so, you avoid charges of plagiarism .