Active Subdomain Enumeration - Questions

I’m completely stumped as to what I’m doing wrong. Yesterday, I was able to get the answer for number 1 and 2, but now, all the commands I do, are not yielding any responses. I have reset the Pwn-Box and generated new IP’s but that didn’t help. Am I doing something wrong? For example, I performed "dig ns inlanefreight.htb @GENERATED IP (which is what I believe I did yesterday) and was going to then use “dig axfr [domain] @[nameserver]”.

Also, the questions asking the FQDN assigned to a certain IP address has me confused.

Any help would be greatly appreciated.