Finding out which NVIDIA graphics card is being used inside a Ubuntu computer is easy using the lspci command:
$ lspci | grep -i nvidia
The lspci program lists all the PCI devices on the system. If there is a NVIDIA graphics card, it should be listed as a VGA compatible controller along with its model name.
Instead of a model name, if you only see NVIDIA Corporation Device, then maybe you are using a card released recently. Update the PCI ID information on your computer and try the command again.
Tried with: lspci 3.1.8 and Ubuntu 12.04.1 LTS