How can I make milk cocoa powder so it does not stick to the top and bottom? A package of milk cocoa powder contains "20% cocoa powder, sugar, emulsifier (soya lecithin), flavouring (vanillin)". I have tried to make cocoa milk drinks to cold milk but the cocoa stuck to the top and the sugar goes to the bottom. With the ready-milk-powder, things go more to the milk more stabily. What is the trick with the manufacturers? Can I do it myself? I have noticed that the ready-cocoa powder contains much smaller sugar particles to my sugar, apparently they use some sort of special sugar, what is that and how can I get such sugar of such fine size?

For me, the price of cocoa is 12 EUR per kg. I do not like the ready made powders (although their kg price is about 5EUR per kg but 20% cocoa content), I like more cocoa. I have heated the drinks and the cocoa and sugar does not stick so much to the top and bottom but my home-made drinks are strikingly different to the manufactured. What is the emulsifier and where can I get it? Is it the trick how the cocoa/sugar -mixture forms more uniformly in the drink?
I do not think your problem is an emulsifier that you are missing, I think it's just basic temperature and technique 'issues'.

Firstly, you will get a better result if you use a liquid chocolate syrup. It's like adding granulated sugar to an iced coffee - it will sweeten the cold liquid a bit, but most of the grains will just get wet and clump together at the bottom and not mix together. That's why using a simple syrup is a better idea, because the solid elements (sugar) have already been incorporated into a liquid form so the cold temperature won't be a detriment to mixing.

However, if you really want to keep using (or not waste) your existing cocoa, you have a few options. You can make a slurry of the cocoa powder. Get a container that can be sealed well and add maybe a teaspoon of the cocoa mix to 3 or 4 tablespoons of milk and shake it vigorously. Once it is well mixed, you can add more cocoa, and more milk as needed to keep it totally liquid. After it is fully incorporated, stir it into the rest of your milk and it should mix completely. 

This other method may not work for cold milk, but it is how I make smooth hot cocoa without having to make a slurry. I take a good quality cocoa and put it in a small bowl and then add granulated sugar - the ratio isn't vital (and I like a sweet, very chocolatey cocoa), but it does have to be enough sugar to fully incorporate with the smooth, powdery cocoa. Basically I am looking to use the grains of sugar to break up the potential clumps of cocoa by having the mixture as thoroughly incorporated as possible, and then stirring very thoroughly as well. I prefer glass mugs so that I can see that I've gotten all that's fallen to the bottom. 

I hope this helps.