The nslookup command is used to troubleshoot a:

The nslookup command is specifically designed to query DNS (Domain Name System) servers. It allows users to obtain domain name or IP address mapping information, as well as other DNS records. When troubleshooting network issues, particularly those related to domain name resolution, nslookup proves invaluable. For instance, if a user is unable to reach a website by its domain name, using nslookup can help verify whether the DNS server is responding correctly and providing the appropriate IP address for that domain.

While DHCP servers manage the allocation of IP addresses within a network and web servers serve content to users, nslookup does not apply to those functions. Similarly, FTP servers manage file transfers over the network, but they do not involve the domain name resolution process that nslookup addresses. The primary focus of nslookup's functionality is on the DNS server, making it the right choice for troubleshooting DNS-related issues specifically.