I'm self-studying for my CISSP and have a lot of specific questions about the various concepts (for example, clarification regarding the * property rule of the basic security model). Is this the appropriate place to ask? Or is this site geared more towards real-life issues?
Yes - CISSP in general is a professional certification, and CISSP holders are expected to be security professionals, so most questions should fit.
In saying that, the only education questions we tend to flag as off topic are the ones which are just "homework" - the cut'n'paste of an exam question straight into the question box.
As Jeff says, make the questions clear - feel free to browse security SE for examples - and you will get much better responses.
Possibly, if they are of sufficient interest to other security experts.
You might try one or two of what you think make the best questions here to see what kind of reception they get -- then proceed (or not) based on that feedback.
I would definitely be clear in the question what your intentions are.