The word جَدَّتك is composed of جَدَّة = grandmother and the suffix ـك which indicate possession of the 2nd pers. sing. (i.e. your). Thus, جَدَّتك = your grandmother
N.B.: There is a mistake in the exercise. It's supposed to be جَدَّتُك (pronounced /d͡ʒə.'dːæ.tʊ.ka/), since your grandmother is the subject of the sentence.
Thank you, AmineHadji, but why the final a in dzadataka ? As I understand it, dzadda is grandmather, and to make it "your, addressing a male" you have to add tak. Is that wrong? is it taka? But I thought the feminine aspect of the noun is already shown in the additional suffix? (forgive my crude imitation of IPA. May I ask how you type in IPA? I'm full of admiration.
Okay, I got this one right. But a couple of lessons ago, يا + name in the beginning of a question before هل in Arabic in a translation exercise from English to Arabic was wrong although the name was first in Arabic. Could you please not use a word order that is marked wrong by yourself?