I gave Volcarona a Power Weight, but when I Defeated a Trainer, Volcarona didn't gain ANYTHING. It was supposed to get 4 HP EV's from the Power Weight!
Ev's do not appear all of a sudden. Instead, they are slowly added up by the time the Pokemon is level 100. So as the levels progress, the EV's are added up, and eventually, you can see the results.
It does not show straight away.
You can see your evs at lv 100
But they will gradually show as you lv up like you could max out speed at lv 23 but you would not have 63 stat poiunts from evs in speed.
But if your lv 50 you may have around 30 extra in speed.
The same goes for ivs.
If your in black and white you can go to someone who can tell you your evs if your worried your missing some or there not showing up.