Rebuild all modules for the currently running kernel:

sudo dkms autoinstall

or for a specific kernel:

sudo dkms autoinstall -k 3.16.4-1-ARCH

To build a specific module for the currently running kernel:

sudo dkms install -m nvidia -v 334.21

or simply:

sudo dkms install nvidia/334.21

To build a module for all kernels:

sudo dkms install nvidia/334.21 --all

sudo  ls /usr/src/linux-headers-* -d | sed -e 's/.*linux-headers-//' | sort -V | tac | sudo xargs -n1 /usr/lib/dkms/dkms_autoinstaller start