Couple commands to export your ssh-key from a yubikey

Creating ssh-key from yubikey

# Assuming you already generated the private key using some other method, this will extract and create a ssh-key OpenSSH format that can be used for authenticating to openssh.

# This is most useful for ECC keys for right now, as ssh-keygen does not read it correctly.

# Lists out what keys you have on the device. Note the "ID" of the key you want
pkcs15-tool --list-public-keys

# Dump it out
pkcs15-tool --read-public-key <id> > my_key.pub

# Convert it to openssh format
ssh-keygen -i -m PKCS8 -f my_key.pub