Getting exact spawn egg of a mob

I've been working on a lil project. And for that I need to be able to get spawn eggs of mobs or a summon command of mobs in the wild. What I mean is let's say there's a zombie with diamond armor and a diamond sword. How do I get the summon / mob egg of that mob? How do I copy over the nbt data of one mob to a summon/mob egg
?