How can I understand that e-mail is not validated on whois contact?

Only e-mail, which is specified in whois contact of Registrant type is subject to verification.

In this case in the "Manage your account" panel the domain has "E-mail not validated" status, which can be viewed:

• in whois contacts list (item "WHOIS contacts" in "Contract" menu),
• On contact editing page ("Contract" menu  →  item "WHOIS contacts → "Modify" link at Registrant contact).

If e-mail is not validated in whois contact, all domains using this contact will also have "E-mail not validated" status.