It doesn't matter unless you're reading out loud. Seriously... Just pick one and go with it....as long as your brain connects the pronunciation you've chosen with the character or place, you're good. And if you're having a discussion with another person about the books, you'll figure out what they're talking about and they will too. My friend and I pronounce DaHara, Jagang, Kahlan, and Nicci differently and don't confuse each other.
My friends and I have read all of the books besides 'The legend Of Magda Searus first confessor' and we just pronounce all their names and words however we think they must be pronounced. The only difficult words to pronounce are the High D'Haran ones which I wish there were more of, it is an amazing language and I wish Terry Had of completed it.
I'm only partway into TotW (Chapter 54 as of this post) and I've always kind of seen the High D'Haran words as somewhat similar in appearance to Dutch or German, so I tend to keep that in mind when I read them.
As for Emperor Jagang; since he's described in something of a Mongolian Warlord caste, I thing "Zha Yang" where the "Zha" is something like a mix of J and Z. It's kind of hard to describe in words but if you know what I'm talking about then awesome.