Hijacked domain

My client had his domain name hijacked by an employee who has the login info and control of the email account associated with the domain name. My client doesn’t really email. How do I restore his control of the domain name? So far I get unhelpful email blather.

Where is the domain actually registered? And what “blather” did they give you? It’s not trivial to regain access to a domain. Proof of ownership is pretty challenging.