The pattern doesn’t call for any specific weight of yarn, but DK would probably be a good one to use.

Here are the instructions for a basic turtleneck with options for crew neck, feather yarn, or feminine waistline noted: https://zenhensart.com/project-instructions/tiny-sweater-...

You can find more about these tiny sweater ornaments here: https://alexisartstudio.com/category/tiny-sweater-ornaments/