What can I with a bottle of chocolate grappa (besides drinking it)?

Mix with compatible flavors or ingredients (Nuts, mint, chile, berries) to make a sauce for ice cream or pound cake.
Use it to spike coffee or hot chocolate.

There is a recipe on this site that combines figs and regular grappa to make a wonderful cake- and that would probably be dreamy with your chocolate version. Brandy chocolate truffles would be another suggestion. Add it to a chocolate ganache, or a pots de creme. What you have there is a chocolate flavored brandy of sorts, so loads of dessert recipes which call for brandy could potentially work. Depending on how adventurous you feel, you can also use it to make homemade ice cream.