Not sure about a jello shot, but a chocolate martini is made with chocolate liqueur, vodka, and ice. Fill a shaker glass with ice, add equal parts of vodka and liqueur, and shake. Make sure you have some cute martini glasses to serve it in.
For jello shots we usually add the liquor of choice with the cold water in the jello recipe. Depending on how strong you want them add 1/4 or 1/2 or 3/4 of the cold water as liquor. pour them into 1 oz cups and let them set up.