Please note that both above solutions will work only if the actual NVIDIA module is loaded.
Check Xorg X server logs
Another place where to find NVIDIA driver version is to consult Xorg X server log files:
# grep "X Driver" /var/log/Xorg.0.log
[ 10.295] (II) NVIDIA dlloader X Driver 352.63 Sat Nov 7 20:29:25 PST 2015
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Retrieve module version
If all above commands fail because you are unable to load NVIDIA module you can always see NVIDIA version number by directly retrieving nvidia.ko module version using modinfo command. The below command will check for NVIDIA driver version under your currently running kernel: