What is the link, if any, between Zero Knowledge Proof (ZKP) and Homomorphic encryption?
There are many.


Homomorphic encryption implies ZK proofs for NP. This is simply because homomorphic encryption implies one-way functions, which imply ZKP for NP.
Homomorphic encryption allows to compile any public-coin zero-knowledge proof into a designated-verifier non-interactive zero-knowledge proof; this was shown in the paper Non-interactive Zero-Knowledge from
Homomorphic Encryption.
Zero-knowledge proofs are not known to imply anything regarding the existence of homomorphic encryption. In fact, only very strong forms of zero-knowledge proofs were very recently shown to imply public-key encryption.
Fully homomorphic encryption can be used to minimize the size of a non-interactive zero-knowledge proof, and reduce it to witness size + polynomial in the security parameter, see this paper.


This is just a sample of the many interplays between the two notions; if you had more specific relations in mind, please clarify.