How to propagate Wi-Fi packets to other interfaces on a router
It highly depends on the (SOHO-) router and its internals if sniffing is possible. Usually Wi-Fi and ethernet ports are separated and you can't sniff Wi-Fi with an external ethernet device. Even if your router contains several ethernet interfaces and all of them are attached to an internal switch, packet capturing of the other ethernet ports is impossible.

Some routers contain an internal sniffer though. My router (AVM Fritz!Box 7490) provides a sniffing feature for diagnosis:



After choosing one or several of the different interfaces and hitting one or several start buttons I get a full capture in Wireshark format.

Your D'link router may contain a similar feature. Or a free firmware with this feature exists for your router.



A second option is a Wi-Fi sniffer attached to the desktop computer.