They’re pretty cartoony but I don’t think they really fit into a “style”. Sugar skull tattoos are pretty common, so the artist should know what you are talking about when you say it. Just find a good artist whose work you like and google some images. A good artist will do what you want, and you’ll know if you like it or not when they draw it up.

sugar skulls are a subject. They come from the day of the dead. Usually they are small decorated sweet breads in real life. As for style, thats up to whoever is drawing it. Ive seen them done in a variety of styles, from full photorealism to old school bold tattoo designs.