Your best bet is to use Chrome's debugger, and to browse the runtime.js of plugins you're interested in. See their onCreate methods - that's where they create all the properties the object will use. You shouldn't use the properties array directly - that really ought to be deleted after onCreate(), but I left it in anyway.
You cannot access properties by the string of their name, because the minifier renames all properties on export and will break that.
Instance variables are stored in an array property called instance_vars IIRC, and behaviors are stored in an array called behavior_insts. The debugger will tell you more.
It's quite unusual to need to know the types of a property - usually you know what it is by assumption (if you get the 'width' property, for example, obviously you're going to get back a number and not a string). However if you need to dynamically determine types, use Javascript's typeof operator.
What are you trying to do? Sounds like you'll have a hard time, especially because of the minifier.