Hi,
I've looked around at the same sort of thing for the carton label fields. From what I can tell, there are certain queries that are hard-coded that pull whatever information is displayed on the labels, and the end users don't have the ability to edit those queries. You can add or remove any fields you want that are already included in those queries though, but I don't know how you'd be able to find a complete list of the fields that you're able to use. It's possible that the field you want is available already, but to add it, you'd need to know how to modify zebra printer code, which can be very ugly. For example, here's a small piece of one of our carton label files:
{PC000;0318,0102,15,15,O,33,B,P2|}
{PC001;0584,0636,10,10,O,33,B,P2|}
{PC002;0388,0581,10,10,O,33,B,P2|}
{PC003;0457,0134,10,10,O,33,B,P2|}
{PC004;0443,0705,15,15,O,33,B,P2|}
{PC005;0370,0139,10,10,O,33,B,P2|}
{PC006;0497,0100,10,10,O,33,B,P2|}
{PC007;0459,0364,10,10,O,33,B,P2|}
{RC000;*ship_via@|}
{RC001;*user@|}
{RC002;*depart_time@|}
{RC003;*est_shpmt_wt@|}
{RC004;*style@|}
{RC005;*x_of_y@|}
{RC006;*to_be_pakd_units@|}
{RC007;Shpmt Wt:|}
The lines starting with PC define the properties of a text area - location, size, etc. The lines starting with RC define the text to go into the area. So for example, the ship_via field will be put in the text area RC000, which will correspond to the formatting defined in the line starting with PC000.
I'm not sure if it'd be the same with your printers. We're using TEC printers, so our format may be different, but hopefully this gives you an idea of what you might have to do. Several months ago when I was trying to figure this out, I spent a couple of days just doing Google searches, and I found a beautiful document that explains all the above codes and what the various numbers mean. You might be able to find something similar for your printers.
Hope that helps!