Preheat oven to 400 degrees F. Lightly spray a baking sheet with cooking spray; set aside. Soak some wooden skewers in a bowl of water for about 15 minutes.
Rinse pork tenderloin with cold water and pat dry with paper towels. Trim off excess fat and silver skin. Cut into 1-inch pieces. Skewer the pieces and place on baking sheet in a single layer. Sprinkle the skewers with the seasoning mix. Broil in the oven for 10 to 15 minutes, turning the skewers halfway.
Put grapes and sherry in a skillet and bring up to a boil. Lower the heat to a simmer and cook until grapes just begin to split and the sauce thickens.
Remove skewers from oven and transfer to a serving platter. Spoon grapes over the pork skewers and serve immediately.