Newer versions of Dolphin (5.0-5179 or later) can extract these certificates automatically. Go to Tools → Perform Online System Update within the emulator.
Understanding and Acquiring clientca.pem : A Guide to Client Authentication
The specific clientca.pem you need depends entirely on the system you are using. It is rarely a "generic" file you can download from a single central source; rather, it is usually part of a specific software package or generated for your unique environment. 1. Most Common Use Case: Dolphin Emulator (Wii Online)
Once acquired, these files must be copied to the User/Wii directory in your Dolphin folder. 2. Enterprise Use Case: Kubernetes and PKI