When using console.log() in node to output the sessionid returned by tls's newSession event, it output the sessionid in the following format -
<SlowBuffer fa de 06 ab 51 d6 30 1b e8 ad 09 14 0e c1 1e eb 56 53 ee 6d b5 ef 9d 99 5d 1a eb 79 dc aa 34 3a>
What format is this? And in what format should I save it to retreive it later?
As already shown in one of your other questions, just use sessionId.toString("hex").
As per the TLS RFC the session ID is a random byte sequence, you can't expect it to be text with some sort of meaning.