You can hand whip Dalgona coffee without a problem, but it will take you a very, very long time and hard labor.  You have to really keep mixing it fast and for a long time for the foam to start forming.  You can also use a hand milk frother which will give you slightly different results, but everyone likes something else.  My daughter likes the Keto Dalgona Coffee topping directly from the kitchen machine, as the froth is much lighter.  My husband on the other side loves the Dalgona Coffee froth from the hand milk frother.  So it is really up to you which way you choose and which way you prefer.