For the P1 Horses and Drakes, equip the pet and hit the letter "O" in game to bring up it's pet window. This will show the exp needed to reach it's next level. P1 pets don't need to be "evolved". They'll automatically level when the exp gain reaches that amount on the pet window. And, if you know how to earn exp for the P1's(won't gain exp if you're hitting blue named mobs), then you know how to level your P1 pets.