There are so many ways to make cold coffee. In this recipe I've used blender to make milk froth, if you have milk frother or mason jar you can use that instead of blender.
Mix hot water, coffee and coco powder well and keep aside. Let it cool for a bit.
In a blender add coffee mixture, sugar, ice-cream and ice and blend for good 4-5 mins.
Enjoy it as is or serve it with some whipping cream on top.
Notes
This recipe yields 3 glasses of cold coffee. You can skip ice if your milk is chilled for that place the milk in freezer for an hour beforehand. You can skip whipping cream but it adds extra creaminess and froth to coffee.