When monitoring your input while recording into Cubase or Nuendo you need to decide if you are going to monitor from the Software or use a hardware monitor that may be available on your audio interface. If you want to use the software or if your interface is not capeable of direct monitoring then you may need to turn off direct monitoring in Cubase/Nuendo.
Do this by going into Devices>Device Setup> and select your audio interface listed below the VST Audio Sytem. In this window UNCHECK the box next to Direct Monitoring. This will enable the software to allow you to monitor and not expect your audio hardware to do it for you.
Also you will need to enable the monitor button found next to the record enable button when you record arm your track. You now should be able to monitor your recording into Cubase or Nuendo.