I am a complety newbie on this one so please forgive me 
I would urgently need tips on how I could manage the synchronisation with a server which accepts e.g. (x,y,z, velocity) and sends me back a confirmation/synchronisation of the movement.
With KeyNodeForwardAction I can move a node but what steps are than needed to get a smooth server controled movement of my objects?
If you want something easy to use, and don’t already have a network architecture:
Darkfrog’s JGN project (do some searching on the forums for it and you’ll find more info) works very well for jME.
If you already have a network architecture or need to interact with other clients:
Use “client-side prediction.”
In simple terms, you let the client do what they are requesting. When the client receives the response from the server, you can then make some adjustments.
For instance, I let a character start walking towards their destination on the client. If they become more than X units away from where the server tells them they are, move them to the correct position, increase/decrease their speed, etc. You may also want to take into account the latency from the server to client and the velocity of the moving object. Speeding bullets may require more work, such as the use of “lag compensation” methods, but I guess that sort of thing is a bit off topic if we’re looking for simple solutions.
Many thanks for info I will go for a client side aproach sending infos to server and accepting them when in tolerance.
But how could I find out via e.g KeyNodeForwardAction when an action has happened.
I only want to send movement info to server when there are actually movements.
I would like to go for a observer like aproach that is sending server pakets only when a state in KeyNodeForward action has changed (moving).
But I have not found any possibility to get infos out of KeyNodeForwardAction.