[SOLVED] Damage over players head

How comes that on some servers you can see the hit damage of your shot over the players head and on others cannot see it. Is this serversided or clientsided? Which CVAR is necessary for this?

The feature you're talking about is called damagetext. Its relatively new - was introduced after 0.8.1. Some servers help us test Xonotic by running nightly builds so they have it. Servers running 0.8.1 don't.

It's both server (detecting damage and sending it to client) and client (actually showing the numbers) side. The client is always downloaded from the server you join even though your menu stays 0.8.1 (or the build you have downloaded). This means you don't have the options in your settings but you can manipulate the cvars through console when connected to a sufficiently recent server. The cvars start with cl_damagetext.

What martin-t said also applies to demos recorded on those servers. Opening those demos will also load the build settings, which can also then be manipulated via console.