Step one: Register and attach a subscription:

# subscription-manager register --auto-attach
Registering to:
Username: xxx
Password: ********
The system has been registered with ID: db829ea7-e0f6-4586-bd0a-d2648681d1d2
The registered system name is:

Step two: Enable Ansible Engine 2.8 repository, assuming the subscription have that available:

# subscription-manager repos --enable ansible-2.8-for-rhel-8-x86_64-rpms
Repository 'ansible-2.8-for-rhel-8-x86_64-rpms' is enabled for this system.

Step three: Install the thing:

# yum -y install ansible

Step four: Profit!

# ansible --version
ansible 2.8.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.6/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.6.8 (default, Jan 11 2019, 02:17:16) [GCC 8.2.1 20180905 (Red Hat 8.2.1-3)]