To check your Pokemon's stats, simply click 'X' to get to your menu, click 'Pokemon' to open up your team's information, and then look at the stats displayed on the top screen. To view your Pokemon's Effort Value spread, click 'Y'.
To view your Pokemon's IV spread, which I believe is what you're asking, you must first become Champion then make it to the Battle Tree. Talk to the Ace Trainer to the right of the entrance to gain access to the judge function. While having the cursor on a Pokemon while using the PC, click the judge button on the lower screen. Your Pokemon's IVs will be displayed on a graph, there will be one of six phrases on each stat depending on the IVs the Pokemon has:
No Good = 0
Decent = 1-15
Pretty Good = 16-25
Very Good = 26-29
Fantastic = 30
Best = 31
If you want to know a Pokemon's exact IVs, try using this calculator.
Sources:
Experience, and this.
