Well when you do sudo npm install -g prismic-cli then npm will install prismic-cli in /usr/local/lib/node_modules/
And in order to check if the package has been installed successfully; you can do this command ls /usr/local/lib/node_modules/ and will list all the packages installed globally.
Generally, if you close your terminal and open it again, you should be able to access prismic CLI command again.
Please let us know if you need any further assistance,
Fares