Nslookup simply uses the first DNS server it detects among all network adapters present in the system.
Run ‘netsh interface ipv4 show dns‘ to display a list of network adapters and the respective DNS addresses (if applicable). You will notice that Nslookup will assume the first DNS address it finds in this list as the DNS server to use.
A graphical way is to go to open ‘Network and Sharing Center’ > ‘Change Adapter Settings’. Take note that however, the order of network adapters shown graphically here may not be the actual order that is read by Windows. This view is simply for viewing the DNS address of each adapter graphically. In order to see the actual order graphically, press the Alt key, click ‘Advanced’, and then click ‘Advanced Settings’. Click the ‘Adapters and Bindings’ and then under ‘Connections’, click the connection you want to modify and raise and lower its position accordingly.
It took me awhile to figure this out, I was wondering why nslookup wasn’t using the DNS address on my active wireless connection. It turns out that there is another adapter that is higher in order that has a wrongly configured DNS address, and nslookup was using the erroneous DNS address to perform its function.