you cant...
but you can make an eevee egg at the daycare center using your jolteon and a ditto.
Jolteon does not evolve, but to get a Jolteon you need a thunderstone to evolve an Eevee into Jolteon.
To get Jolteon, you must first catch an Eevee, and then evolve it with a thunderstone. Go to your back, go to items, select thunderstone, click use, then click your eevee. Eevee must be in your party if you wish to evolve it :)
you can evolve pikachu into Raichu and Eevee into Jolteon
Any electric Pokemon that can evolve and eevee into Jolteon.
use a thunder stone
just use a thunderstone
get an eevee and evolve it into a thunderstone
Jolteon cannot evolve into Leafeon. Eevee can evolve into leafeon, but not Jolteon. You have to make eggs to get more eevees so you can evolve them.
pikachu to raichu eevee to jolteon
Use a thunderstone.
Flareon, Jolteon and Vaporeon.
You can't naturally obtain jolteon in emerald. First you would have to get an eevee. Unlike other games an eevee isn't given to you. Trade with a friend to get an eevee or jolteon. Keep in mind you need a thunder stone to evolve eevee