He has the ability to cook delicious food. ✔​

She doesn't know her ability. ✔​

I want any ability. ---> I want to improve my abilities.

=> This sentence is okay. This is another way of saying it. 

B. Make these sentences into English.

작은 걸로 주세요.

Please give me a small one. ✔​

작은 사이즈 여기 있습니다.

Here's the small size. ✔​

탈의실은 저쪽에 있어요.

Dressing room is over there. ✔​