Reach level 3 to learn Corruption, then cast it on a Training Dummy in New Tinkertown 5 times.
I'm not at all surprised that a warlock like you fought your way out of Gnomeregan. Few people, even among the gnomes, truly understand the nature of the power we wield. As you become more powerful, you're going to start hearing the fel voices revealing their secrets to you, teaching you new spells. I want you to go get some more experience. Once you learn something new, show me.