This one. But you might have to work up to it.
Two other resources I'd recommend are
Personality Type: An Owner's Manual for a distilled explanation and
8 Keys to Self Leadership for a more personal growth-oriented approach to the functions.
I havent read the whol book 8 keys to leadership, but it seems to introduce this weird big picture on typology based on those some pages i did read. Also what pissed me off with it was that it claims that jung talked about everyone having 8 functions, when jung didnt even talk about there being 8 functions, but 4, which are oriented introverted or extraverted when developed(except inferior automatically opposite from dom, because its most heavily repressed) and are "chained"(used through) to other more developed functions before they are properly developed. Because for example inferior Se might be used in the field of Ni and this would be extraversion working in the limits of inner world, according to this books author(and with other books author) it would be same as using Si, but the definition of Si is bit different..
I got that other book and it kinda has the same problem, there are lots of good stuff in the book, but some important aspects are missing or are twisted around. Also this book 'personality type: owners manual' claims she found some physiological basis for functions, but those are proven wrong.
The problem with these newer books on typology in general is that they dont give you understanding on how these functions play in your psyche and you dont get a proper big picture of them, but give you more like "when you decide that something is important, you use feeling function" type of dummy descriptions.
Now its true that jungs 'psychological types' is difficult to read since its not originally aimed for general population, but more for professionals, so its not something that you can just read and understand in its whole complexity, but you should get back to it few times, especially the definitions chapter should be read many many times, because you might notice after reading something for the fifth time that now you really got what it meant for the first time, and it might help you to understand something else.. But if you want quality reading, this is the only real choise. Like that fusion of functions to others or imo what are the most important aspects of typology, you wont find in any new self help books(like those two posted by bologna).
But if you just want quick not so comprehensive answers to something, then some of these new self help books might be better for you.
I suggest reading this:
http://www.nyaap.org/jung-lexicon/a
And btw this isnt so much reply to you bologna, but to op