Student or Learner
''We all know the “rules” for the job application and interviewing process by now: proofread your resume 100 times, dress for the job you want...''
Could you tell me why 'know' is used but now 'have known' with 'by now.'?
"Have known" is incorrect regardless of any use of 'by now'. (I assume you mean "but not 'have known'").
If someone wants to know if you know the rules, they might ask, "Have you read the rules" or "Have you learnt the rules?", but there's no place for "Have you known the rules?".