I am covering a mud cake with fondant. Do I just use sugar syrup or jam to stick the fondant to the cake, or can I use a chocolate frosting as the adhesive?

Any suggestions and welcome! Thanks!

cakes, the answer is all of the above. Just whatever works for you. I've used sugar syrup, whiskey, ganache, and buttercream to stick fondant to mudcakes.
cheers
Nati