That is an onion holder slicing guide (also frequently sold as a meat tenderizer / vegetable slicing comb).

Primary Functions

• Onion & Vegetable Slicing Guide: You press the metal tines vertically down into a whole onion, tomato, potato, or lemon. The long stainless-steel prongs hold the food securely in place and serve as cutting channels, letting you guide your knife between the tines to slice uniform, even rounds without touching or smelling like the onion.
• Meat Tenderizer: Squeezing the handle and pressing the sharp tines repeatedly into steaks, chicken breasts, or pork chops pierces the muscle fibers, helping marinate and tenderize tougher cuts of meat.
• Hand Guard: It acts as a safety barrier to keep your fingers well clear of the knife blade while cutting round or slippery ingredients.