Whois version

Ubuntu is no rolling release. Packages in older Ubuntu releases usually stay at the version which was the current one when that Ubuntu release was published.
Newer versions of packages will only be provided with newer Ubuntu releases.
Ubuntu 18.04 (to be published next April) will probably contain whois version 5.2.19.

Only for specific packages (e.g. the kernel, firefox, java and similar packages) an update of the published version is done, or in case that a package has severe bugs or if a new version brings important functional improvement.

If you have a problem with whois version 5.2.11 in xenial, you are invited to create a bug report requesting an update. Please add a statement why you think that an upgrade is necessary. The developers will then decide what to do.

What is in the new version that you need so badly?

Hi, when doing a whois lookup from terminal on a domain the full version don't show up which is very annoying, therefore I think a upgrade would be great. As you can see in the link. As a malware hunter when doing lots of lookups it would be great https://paste.ubuntu.com/26237723/ as you scan see in the paste the first whois is from the current version and the other from domaintools which gives the same output as the newer version 5.2.19

If you need the current version in xenial, you could try manually downloading and installing the newest version for bionic.

Generally, installing a package in the version for a newer Ubuntu release on an older one can work well, but may also fail miserably because of broken dependencies. The whois package does not have any problematic dependencies, so I am quite confident that this will work.

Try downloading the whois_5.2.19_*.deb package suitable for your processor architecture from https://launchpad.net/ubuntu/+archive/primary/+sourcepub/8559882/+listing-archive-extra and install it with a command like
sudo dpkg --install whois_5.2.19_*.deb