What data is displayed on civilian ATC radar screens?
There are a few different ATC Systems and Radar Screens being used throughout the world, so there will be no set standard which applies globally, as vendors and setup differ.

The ATC screen can be adjusted to show what information the controller needs, and some items are universal to all positions being served (Callsign, Speed, Altitude, Assigned Altitude), some items are not required on each position to be displayed on the radar tag (Squawk, Routing, Aircraft Type, Wake Turbulence Category).

Some examples:

Source: www.andreas-milde.de

Source: www.euroscope.hu / Air Traffic Simulation Client

Source: fluglotse.wordpress.com