I was wonder if there is any manual describing how a client application should communicate with a q4 server (a document where it say what commands etc are avaible for communication between the client and server).

Are you talking about the serverinfo communication used by serverbrowsers and scorebots etc, or about how a q4 client goes about connecting to a q4 server?

I wouldnt be surprised if the low-level network stuff of the q4 client <-> server comms is going to be encrypted to prevent cheats, however the higher level (ingame) protocol is pretty much defined by the SDK code.

The serverinfo querying etc is pretty standard across the quake games, theres lots of reference implementations and docs etc (try qstat as a starting point, maybe).

i am talking about the server info  communication used by serverbrowsers, so all the info is avaible in the sdk ?