Go to "Manage Jenkins" > "Scripts Console" and run below command.
def creds = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
com.cloudbees.plugins.credentials.Credentials.class
)
for (c in creds) {
println(c.id)
if (c.properties.username) {
println(" description: " + c.description)
}
if (c.properties.username) {
println(" username: " + c.username)
}
if (c.properties.password) {
println(" password: " + c.password)
}
if (c.properties.passphrase) {
println(" passphrase: " + c.passphrase)
}
if (c.properties.secret) {
println(" secret: " + c.secret)
}
if (c.properties.privateKeySource) {
println(" privateKey: " + c.getPrivateKey())
}
println("")
}