There are several different models of Netgear Nighthawk routers, however they are all of the ac wireless type.
Unless the router is configured to provide a a/b/g/n wireless signal in addition to ac, the iPad 2 will not be able to connect to it. The iPad 2 does not support ac type wireless.
Assuming it is producing a a/b/g/n signal type, then I would start by resetting the network settings of the iPad. If the wifi network being produced by the router has the same name as the old router but a different password, the iPad may also encounter issues while connecting.
Try going into Settings->General->Reset->Reset Network Settings. This should clear the wifi settings, and reboot the iPad. Once it starts up again, you can attempt to connect to the wifi network again.