When you unlock your Subclass and level it to 85, you can do the Awakening quest on the sub, and towards the end of that quest your sub will get the same compensation for enchanted skills as your main. About 3/4 down this page you can see how many Lesser Giant's Essences you will get per enchantment level: http://power.plaync.co.kr/lineage2/%EC%8A%A4%ED%82%AC+%EA%B0%95%ED%99%94