Have your grill going at a medium heat. If you have a temperature gauge, aim for a range of 350°F to 375°F. Have racks set to a direct and an indirect position.
Place the Nutella and cream in a small bowl and whisk until as smooth as possible; they might not quite come together before heating. Scrape into a small saucepan that can go on the grill and set on indirect area. Close grill and allow to heat up, whisking occasionally, until smooth and hot.
Meanwhile, thread the fruit and cake onto skewers and place on direct grill rack and heat quickly just until cake takes on some grill marks, flip over and cook the other side. You can close grill for a few moments as you cook the skewers, but you must keep an eye as these cook fast.
Serve immediately. I suggest pouring fondue in small individual cups and give everyone a skewer and a fork. Use fork to remove items from the skewer and then use to pierce and dip each piece of fruit or cake into the fondue.
Recipe by Bakepedia at https://www.bakepedia.com/nutella-fondue-grilled-fruit-cake-kebobs/