Is citing required for Tag wikis that come from other sources? If so, how does one do it? I am just curious as there is plenty of info out there and if something is a direct quote, should it be cited?
Tag wiki content should be cited just as you would if you were posting it as an answer. You'd quote a few sentences with a link back to the source.
If you need to quote more than three sentences, that's already too much. (Three is just a rule of thumb and pinkie.)
Better no more than that and just fill out the rest of the tag wiki with more Super User specific information such as related tags, top list of questions, how best to use the tag on a question, etc.