To obtain their public key, import them from email they have sent to you and that includes it. Alternatively, you can try to discover their public key on a directory.
Zo byšće jeho zjawny kluč dóstał, importujće jeho z mejlki, kotruž je wam pósłał a to jón zasadźi. Alternatiwnje móžeće spytać, jeho zjawny kluč w zapisu namakać.