PKCS#8

PKCS8¹ in usually used as syntax of unencrypted RSA private key,

you can simply generate a RSA key via openssl:

nix-shell -p openssl
[nix-shell:/tmp]$ openssl genpkey -algorithm rsa -out test.key
[nix-shell:/tmp]$ cat test.key
-----BEGIN PRIVATE KEY-----
MIIEvwIBADANBgkqhkiG9w0BAQEFAASCBKkwggSlAgEAAoIBAQC6LU2ZNdy32+HL
...
c581/XSSIu1kZpptICNGM4MiDJyGoysNX7417wXgwr8YEb6fbMAMGjjYKbF9BlpY
yRdkNiEmIKL4/ZQoTLdyQR4vJQ==
-----END PRIVATE KEY-----

[nix-shell:/tmp]$ openssl rsa -in test.key -noout -text
RSA Private-Key: (2048 bit, 2 primes)
modulus:
    00:e9:6a:68:ab:7b:73:f0:14:72:24:e5:35:f1:c2:
    ...
publicExponent: 65537 (0x10001)
privateExponent:
    00:c0:6f:a1:11:d7:ba:f2:f0:f8:56:20:be:c3:ad:
    ...
prime1:
    00:fb:d7:d5:fd:2c:b5:b2:cd:92:b0:ea:60:83:29:
    ...
prime2:
    ...
exponent1:
    00:e5:8f:16:15:92:9d:85:00:71:c8:25:bc:17:92:
    ...
exponent2:
    3e:6e:01:ad:b7:63:36:96:90:f9:ed:38:c4:10:bf:
    ...
coefficient:
    00:89:e1:69:2b:78:97:a9:91:88:39:7a:75:08:f0:
    ...

The output is readable text but the original PKCS#8 is in Abstract Syntax Notation One(ASN.1)² syntax and DER encoded.

Private key is kind of too long as example, lets use public key to explain.