EV training works the same way as any generation. Plus it works on any Pokemon, regarding there stats already.
Different Pokemon gives different EV's in value and stats (you can search up the Pokemon or look at this on the website as well. A Pokemon can have a total of 510 EV's in total. Also, a Pokemon can have 255 EV's at max in one stat. But, 4 EV's = 1 stat point. Therefore, it is more useful to train the Pokemon with 252 EV's in one stat since 255 is not divisible by 4 (wasting the use of training).
For example, you might want to train Blaziken in different stats. Let's say you want to fully train Blaziken's speed EV's. Look for some Pokemon who can give speed EV's. Some Pokemon include Joltik, Emolga, Swanna, Solosis - although there are tons more - these are just some Pokemon that you can find in White. Therefore, you will need to kill a total of 252 Joltik's (or the others) to receive 63 more stat points. (252/4 = 63 stat points). But, some Pokemon can give you more such as Emolga. Emolga gives 2 speed EV's so you will only need to kill 126 of them.
If you find this is a boring method, luckily, there are some items that can help:
HP Up = HP
Protein = Attack
Iron = Defence
Calcium = Sp. Atk.
Zinc = Sp. Def.
Carbos = Speed
Each use will give you "10 EV's to the corresponding stat". You can only use 10 at max per stat. However, these will only work on the first 100 EV's. For example, if you started Blaziken's speed EV training and already got to 60 EV's, you can only use 4 more carbos (*not 10).
EV training can be quite confusing so feel free to comment on any misunderstandings.
Good Luck! Hope I helped! :)
