I'm working with text lines in a Tikz Header, and all I need is the options for anchor= (eg. anchor=north) and I can't find a basic list of anchor options anywhere
The manual is the general reference. As Rowan Parkinson mentions in a comment, you can find it by issuing
texdoc tikz from a terminal/command prompt. Or you can find the PDF on CTAN or texdoc.net. There is also an HTML-version at https://tikz.dev/ (not created by the package maintainers).
However, as the manual covers a lot, it is quite large (1300 pages), and it can sometimes be hard to find stuff there. What you're after, the choices for
anchor, is described in chapter 71 about the Shape library (which is in part V Libraries, if you look at the contents). Each different node shape may have differently named anchors, so for each shape described in that chapter, you'll find a diagram such as this one, naming the anchors and indicating where on the shape they are: