I am making a cake this weekend that I want to look like a whole watermelon filled with fruit salad. The fruit salad will just be fondant shaped melon balls on top, but i'd like them to look wet. how could I do this?

The best way to make a product look wet would be to spray with melted Cocoa Butter. You can spray it with a airbrush system or just paint it on. Once dry it will look a bit waxy. Or you could brush it with liquified piping gel from Wilton. All you have to do is microwave if for about 30 seconds.

clear pipping gel gives a really shiny wet look, apricot jam melted in a little bit of boiling water and strained gives a good result though not as shiny/wet looking as the gel

I believe there is a product called "edible lacquer" that would dry and not be sticky.

thank you