Nslookup: command not found error on RHEL/CentOS 7

The minimal install likely did not come with the bind-utils package, which I believe contains nslookup.

You can install bind-utils with:

sudo yum install bind-utils

In general, you can search for what package provides a command using the yum provides command:

sudo yum provides '*bin/nslookup'

For those using DEBIAN, the package to use is dnsutils and the installation process should be, initiated with:

sudo apt-get install dnsutils -y

According to other users it is the same for Ubuntu