"저는 공부를 합니다."
I guess it's the ending of the stem of the verb 공부하다. But I'm not sure about it yet. I've seen a lot of verb stems ending with 하. At this speech level 합쇼체, when the verb stem ends with a vowel the ending is -ㅂ니다 and when the stem verb ends with a consonant the ending is -습니다. I hope it helps.