You can look up their associated email using a pgp key server, if they published it.
https://pgp.mit.edu/
If you are a windows user:
https://www.gpg4win.org/index.html
Otherwise, Kleopatra
Please Login to reply.
Thanks, bud! I found this pretty neat write up on the basics of PGP encryption
https://www.varonis.com/blog/pgp-encryption