Recently, I found a citation to "DIO 38.6 (2)" in a text. I know Dio as both a JoJo villain and the author of "Roman History", however I do not understand what specifically the citation means. Is the 38 the volume, the .6 the page, and (2) the line number?
The specific text I'm referring to is "Caesar paid little attention and fixed a day for the passage of the law."
You're close. Page number won't come into it, because that will differ from edition to edition. Classical citations are designed so that they will be uniform across all editions. That citation is for Dio (Historia Romana), book 38, section 6, line 2. See here.