For me, that would be IT for the company using the product (Tridion Sites or Docs in this case).

Knowing what I know now, at least for Sites, the "Administrators" should be members of the Admin group(s). If the "task" workflow was more popular, I'd even send a task to the admin with the message details.

But nowadays, I'm assuming email or chat integration would be a better way to "contact" an admin.

Some companies have 3rd parties or other externals administering a given system. In that case, admin should be clear based on the given system (whoever you normally ask for system help from for that system). 

For me, that would be IT for the company using the product (Tridion Sites or Docs in this case).

Knowing what I know now, at least for Sites, the "Administrators" should be members of the Admin group(s). If the "task" workflow was more popular, I'd even send a task to the admin with the message details.

But nowadays, I'm assuming email or chat integration would be a better way to "contact" an admin.

Some companies have 3rd parties or other externals administering a given system. In that case, admin should be clear based on the given system (whoever you normally ask for system help from for that system).