See certificate issuer

openssl x509 -in /etc/letsencrypt/live/5d61057e5e1f.sn.mynetname.net/fullchain.pem -text

or:

openssl x509 -in /etc/letsencrypt/live/5d61057e5e1f.sn.mynetname.net/fullchain.pem -text | grep "Issuer:\|Subject:"

another:

openssl x509 -in /etc/letsencrypt/live/5d61057e5e1f.sn.mynetname.net/fullchain.pem -noout -issuer
openssl x509 -in /etc/letsencrypt/live/5d61057e5e1f.sn.mynetname.net/fullchain.pem -noout -subject