TBH I don't think I audit to clauses, certainly not tick boxing. I refer to the relevant clause, which in our company could be 9001 or another since there are customer contracted standards to be used plus a few company or stakeholder selected ones. For example risk might be iso 31000 or AQAP 2070 or perhaps something else.
I believe I only use the standards as a guide but then I've learnt auditing mostly from doing it and what I've learnt from here and other recommended sources (often recommended on here). I'm not sure exactly what is meant by auditing by clause.
I've got my copies of ISO 9001 in a few places for referral. A5 copy in my filofax (yes I'm afraid I do analogue as well as digital), A4 in my home office and pdf copies on various devices. There's no way round referring to them when needed.
The memory thing is just to shortcut. Example, team discussing a matter and someone points a colleague to check the standard, it's handy to be able to direct straight to the right clause from memory. That won't stop you referring back to a copy when needed. Also, I think knowing the standard doesn't mean understanding it or applying it.
for someone who didn't use the standard.
