Hi,
You can download the CTI Client Adapter from your Cloud for Customer tenant by going to the Download section.
If it does not work, please report an incident though the help center.
If you are looking to extend the standard CTI features provided by SAP, you will need the CTI Connector project. You can download this from Service Marketplace using this link (or search for CTI Connector under "Search for Software Downloads") -
Best Regards,
Venki Subramanian