If you are querying DNS with a FQDN (system hostname or alias) then you are requesting the IP address of that system. This would be recorded as an A resource record in the forward lookup zone for the Authoritative DNS server for this system. The forward lookup zone provides this conversion from the meaningful name we use to an IP address (which is what really matters).
The reverse lookup zone mainly contains PTR (Pointer Records) and allows you to query the DNS server with an IP address to determine the system hostname. Not all IP addresses will have a PTR - some people will definitely not want you to be able to reverse lookup an IP address!
dig -x <IP address>