G code is G code, the basic commands are the same for all machines. In some cases there are machine specific commands, and these won't be found in generic lists, the factory manuals are the best resource for this. Many times you can find machine specific G code on line with a Google search.
You can perform just about any function possible on any machine with a half dozen or so commands. The basic command format is Gn Xn.nnn Yn.nnn Zn.nnn Fn.n where Gn is the command number, X, Y, Z are the axis target positions, and F is the feed speed. M codes control things like the spindle and coolant. That's really all there is to it as far as the command set goes.
If the factory manuals are available for the machines in the shop, that would be the place to start. Look at the currently loaded programs and any others that may be around the shop.
Here is a generic listing. https://en.wikipedia.org/wiki/G-code