Hi @swanhong CoefPackedPlaintext is currently supported only for BGV and BFV (for the case where numbers modulo t are encoded). We have not seen yet a need for a coefficient encoding in CKKS (as a user feature). All use cases we have seen typically work with the CKKSPackedEncoding encoding.
The coefficient encoding internally comes up in CKKS bootstrapping or scheme switching from CKKS ↔ FHEW, but these are handled automatically by the library using methods like SlotsToCoef (still operating on plaintexts encoded with CKKSPackedEncoding) I suggest waiting for the v1.1 release where you will see how scheme switching is done.