This is something i've always wondered.... i've actually DMed NWN quite a bit, but my actual knowledge of the DM client is still pretty basic.

Can DMs easily(I mean at a glance) tell a characters deity feild, or what spells he has prepared?

I don't think so.

We have customized widgets to do all kinds of stuff. Quickly checking your deity field is one of them; this is particularly helpful for sorting out why new players are getting divine spell failure (often they have typos in their deity field). Examining the spells that a character has prepared could be done, but it's more trouble than it's worth.

If a non-cleric has entered a diety in their field, but has a change of faith, can it be changed in the diety field?

Yes.

Very easily. Just get one us to do it in-game. Deity changes for characters that aren't divine spellcasters should be fairly speedy. (Clerics or Paladins or Druids who want to "switch deities" will have a harder time, because their new deity won't accept them until they have proven that they're going to be more loyal this time around.)

Arkov We have customized widgets to do all kinds of stuff. Quickly checking your deity field is one of them; this is particularly helpful for sorting out why new players are getting divine spell failure (often they have typos in their deity field). Examining the spells that a character has prepared could be done, but it's more trouble than it's worth.

There is a very simple scripted way of duplicating a PC. Then you simply possess the NPC copy of the PC and open up your spellbook. You'll see all the PC's prepped spells.

I think that's not too much trouble, but yes, probably more effort than it's worth.

Oh! Right, yes, we can do that. That requires a bit of work though; it's not something that we can do on the fly (we can view your deity and a bunch of other information, for example, just by zapping you with an Examination Widget).