You should be able to get some logs by looking into USER_HOME_DIR/.sfdx/sfdx.log .

If you are on macOS then simply cd into the home directory using cd $HOME and then cd again to the .sfdx folder . 

You will find sfdx.log file if you open the .sfdx folder .This should have more info for you .

If you are behind the firewall , then update your environment variables as per the below instructions 

https://developer.salesforce.com/docs/atlas.en-us.sfdx_setup.meta/sfdx_setup/sfdx_setup_install_cli_firewall.htm