This is a jukugo word, which usually means on'yomi readings from the kanji. 目玉, however, is an exception. Perhaps this is because it includes a body part (the eye) in it, which often makes a word switch to kun'yomi readings. Either way, it doesn't matter too much. Both the readings you learned for the kanji in this word are the kun'yomi, meaning you should know how to read this one. Just make sure you watch out for the rendaku.
I’ll use these potatoes for the snowman’s eyeballs.
The princess' hobby is to collect eyeballs.
I think these grapes look like monster eyeballs.