For the milkshake: Combine 1 cup water and the granulated sugar in a small saucepan and cook over medium-high heat, stirring until the sugar dissolves. Add the cinnamon stick and orange zest and let the mixture sit until the flavors infuse, about 5 minutes. Discard the cinnamon stick. Add the instant coffee and stir until completely dissolved. Let cool.
Transfer the infused simple syrup and the ice cream to a blender. Blend until smooth. Serve immediately, or keep in the freezer until ready to serve.
For the optional garnishes: Whip the cream to soft peaks. Add the powdered sugar and continue to whip to stiff peaks. Dollop each shake with the whipped cream and dust with ground cinnamon to serve.