That error sounds like it might be because DWARF is not telling LLDB where to find your self object. Given the nature of Swift, LLDB needs to know the type of self in order to be able to inject an expression inside your local scope.
One way to find out if that is your problem is to do at the LLDB prompt:
(lldb) frame variable -L self
You are probably going to not see a location for it. Worth filling a bug report for, just to track your specific repro case.
Anyway, to get to the bulk of your question. In Swift, there is no language-sanctioned mechanism for “print description” like for ObjC, so while you can type po self, unless self is an Objective-C type, you will pretty much see the same thing that “p self” or even “frame variable self” would tell you – which is entirely based on the LLDB data formatters mechanism. If you want to hook into that to customize the way your Swift objects look, the obligatory reference is: http://lldb.llvm.org/varformats.html