How do I connect landline to NighthawK AX2400

[SevignyStudio]

There is no telephone jack to connect landline

[FURRYe38]

IF you don't see any phone jack in back of this unit, means this unit never supported any land line support. 

What model NG product are you referring too? AX2400 isn't a model #. 

[plemans]

If you're needing a landline, you'd need a modem with that capability or  you'd need to subscribe to a VOIP service that connects via ethernet/wifi.