Okey thank you

I have tried a few different skill trees, so maybe I can help a little. I can be wrong.

Fire- nice one to use for most general battles, as one of the first attacks you get from putting points in gives an attack that hits multiple enemies. To my knowledge it is more magic related, the same with Light and Shadow trees, which means they would be good with pets that use magic for their attacks and have high intelligence.
(Some pets are magic users and some physical, probably the easiest way to find out which is which would be to look at the info from the focus attack while in a battle. With stats and proficiencies you can change which one magic or physical is stronger if you mix the two on one pet. Me, I just go with something that compliments what mine already are.) Hitting multiple targets helps get through fights quickly, but on one occasion so far in the game is actually a very bad idea.

Earth-I don't use a lot in battle, it is more physical based and makes I heard makes your enemies target that pet.

Light- I like this one, it is int based, and its attacks have the chance of healing the party. Not much but every little bit can help. The second from this tree does damage to multiple enemies, as well as heals, again very handy. Unlike most people my first pet (the tank so to speak) is my light pet, and one of the damage pets, my entire team is damage pets really. It means I use lots of potions and I struggle on boss fights, but I love the speed at which they knock enemies down, and if I do it fast enough I usually don't use as many potions as you might expect.

Shadow- Also a handy one as similar to light it is int based and its attacks will provide ways to heal the user. This along with Earth was one of the suggested ones for the tank. In the team set up thread.

Wind-I have found a liking of this one too. The first wind attack causes deep wounds on an enemy that will affect them on the next turn. Sometimes it will go into effect for multiple turns as well, and sometimes using the same attack will make it happen again, so you can have multiple deep wounds affecting an enemy at once. The second attack I think like the second fire one will give a boost your pets damage for a set number of rounds, I don't know how much it effects, but it can be helpful. this one is Str based

Frost-also str based. This one is handy. Neither of the first two attacks will hit multiple enemies though. Mostly it is used to increase the pets damage a little or to decrease the enemies mitigation (defense against attacks) a little both apply to physical.