NetAddr::Ip::Util doesn't actually perform any look-ups. It just helps you convert between the different representations of ip address (ascii vs. binary, IPv4 vs. IPv6).

The basic way to find a host's IPv6 address is to use nslookup and query the AAAA record. For instance:

$  nslookup -q=AAAA pnrpv2.ipv6.microsoft.com
...(my DNS server details omitted)...

Non-authoritative answer:
pnrpv2.ipv6.microsoft.com       has AAAA address 2002:4136:e383::4136:
+e383
$
[download]

In theory, you can perform a reverse look-up for this IPv6 address by using:

$ nslookup -q=PTR 3.8.3.e.6.3.1.4.3.8.3.e.6.3.1.4.2.0.0.2.ip6.arpa.
[download]

Each hex digit of the IPv6 address is separated by a dot (.) and is specified in reverse order.