The VPVehicleToolkit component contains examples on reading the data from the vehicle, such as the acceleration. Check out the source code of VPVehicleToolkit for reference.
Check out this answer on how to read data from the wheels. Here is the reference for the WheelState class with all the available data.
All telemetry data (except wheels) is exposed in the Data Bus.
The road grade is computed internally in VPTelemetry and it's not exposed.