The exact configuration for uploading your files to a given CDN will depend on your CDN of choice. The only folder you need to host on your CDN is the contents of .next/static/, which should be uploaded as _next/static/ as the above URL request indicates. Do not upload the rest of your .next/ folder, as you should not expose your server code and other configuration to the public.
While assetPrefix covers requests to _next/static, it does not influence the following paths:
Files in the public folder; if you want to serve those assets over a CDN, you'll have to introduce the prefix yourself