Given that you have an HD44780, you could determine which pins on the I/O connector correspond with the pins on the HD44780. If you find that the two 'E' pins correspond with the 'E' pins on the controller IC's, that will tell you something.

If you put a 1-Kohm resistor in series with the wiper on a 20K-ohm pot between Vcc and Vee, whatever that is, you can probably find a level at which you have adequate contrast for the LCD somewhere in thta range. If you set the wiper to the middle, and go one volt in one direction, and then one volt in the other, until you encounter a visible change in the display, that will tell you whether it requires a positive or a negative bias voltage.

It's not always easy, but, if the LCD module you're using is still being sold, you should be able to get some sort of data sheet. If the controller IC is clearly identifiable, the IC manufacturer's data sheet should tell you all you need.

RE