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.
Aby jogo zjawny kluc dostał, importěrujśo jogo z mejlki, kótaruž jo wam pósłał a to jen zasajźijo. Alternatiwnje móžośo wopytaś, jogo zjawny kluc w zapisu namakaś.