In this paper we continue to speak about the concept of Self-Sovereign Identity (SSI), but not in the cases of IoT devices as it was in previous works [1]. The main purpose of this research is the usage of digital identity in two cases: a) SSI of a single person in Knowledge based system “Experts Ledger” and b) SSI of a company and candidate in HR matching systems. Though these two systems are developed for different issues, the idea of SSI in both is similar. The overview of these systems is done, and the pros and cons of using SSI with the relation of Zero-Knowledge Proof (ZKP) in each of them is made.