Quote Originally Posted by Raistlin View Post
I don't remember ever trying that myself, but I don't see why not. Before you go trying it to learn a very difficult Enemy Skill, it'd be easy enough to test out by Manipulating one of the enemies on the world map to cast an Enemy Skill (White Wind by one of the enemies near Fort Condor, for instance).
You don't really need to test this. Pandora's Box is a move that is only used once by an enemy, and it is cast on your whole party (3 characters). If you couldn't learn it on a single character who had more than one equipped, it would be impossible to learn on all 4 materia. And it is possible to learn every enemy skill on every materia.

The real kicker is this: If you have a single character with 2 Enemy Skill Materia equipped, but one has a skill learned and the other does not, when that skill is used against you, you will not learn it on the other one.

Example: Cloud has equipped two Enemy Skill Materia. One brand-new, and one which knows Matra Magic. An enemy casts Matra Magic on Cloud. The empty ES Materia will not learn Matra Magic.