Can one build a Quetzal Palace in your 2nd City to get a 3rd or fourth City? Or to get 2+ Cities does one need to develop Quetzal Palace in the main City?
Just from your main city
so no good reason to builda Q Palace in any other city then?
If you want to found a new colony, you can do it from any of your cities where the level of the Quetzal Palace is the highest, which in most cases is the Quetzal Palace in the main city.
It makes sense to build the Quetzal Palace in other cities if you want to recruit advanced units there, as some units require certain level of this building:
Jaguar Warrior (Quetzal Palace lvl 1)
Atlant (Quetzal Palace lvl 2)
Ek Chuah (Quetzal Palace lvl 3).
Sure, you can recruit these units in your main city only, in which case the Quetzal Palace in colonies would only be good for gaining some extra pts.
Krymac and Gaviotta are right. I'll proceed to close the thread since I think the question has been answered, don't hesitate to open a new one if you have further questions