Instead of learning this enemyskill on disc 3 by defeating jenova-life you should do it by defeating somthing much much much easier.

preparations-:

you need, enemyskill materia , good defence sense materia and a few potions.

finding the creature-:

when you just got out of the corel prison and earned the buggy, hop in the buggy and drive around the sandy area outside the prison until you face a strange 3 headed grifon-like bird.

the fight-:

To make sure this is the correct monster use sense on it and it should say the name harpy. This creature has around 800hp.Make your atacks fine by damaging the harpy then use sense again to see the hp.If its around 100hp then brace yourself for the aqualung atack.The aqualung atack will take 500-600hp to the party.when you learn the skill use it and wipe it out.

Congrtaulations you just learned one of the best skills on the game.

warning! do not run away from the fight after learning it then you will lose the skill.