Is it just an extender, or is it a full router?
One way to tell is if it has the ability to provide DHCP services, such as assigning IP addresses. If it has a configuration option for setting up DHCP, then it is capable of being a router. If it is in Router mode it will block Bonjour traffic between devices talking to the other Router and those talking to this router.
You want just one active router in your home, and that one active router is responsible for DHCP services.
Another way, would be to make sure you are talking to the extender, and then using the Bonjour Browser. If you can see items that are connected to the other Netgear device, then the extender is not blocking Bonjour traffic, and if it is not blocking Bonjour traffic, it cannot be in Router mode.
If you Option-Click on the WiFi icon on your Mac menu bar, you will see the BSSID for the WiFi device you are talking to. Since you have 2 WiFi devices they will each have their own unique BSSID numbers. With some experimentation, you should be able to figure out which BSSID belongs to the Netgear Router and which belongs to the extender. That is one way to know which device you are currently talking to and then verify you are seeing Bonjour traffic from devices attached to the Netgear router. And traffic going the other way.