I’m memorizing the whole song.
Please give me the whole cow, not half.
This cake is filled entirely with apples.
If you go to (ごと) a circle, you need to go to it in its entirety. That means you have to circle around the whole thing. Otherwise, it isn't even a circle. It's like a line or a squiggle or something.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading, so you should be able to read this too!