WHY DO I NEED TO KNOW MY SIM PIN?

This post would make more sense if you explain why you are asking about a PUK or SIM PIN?

Are you being asked if you want to set one? 

Are you being told you need to enter one to use service? 

Do you have to set one up?  - no.

A PUK, or SIM lock is to prevent someone from taking your sim card putting it in another device and using your service.  

  Setting up the esim prevents a stolen sim. 

PUK is either on your online account under device management, or you have to call AT&T and ask for it. No there is not a default p u k number

Thanks.  The reason I'm asking is:

I was in the Apple Store yesterday.  I had to buy a new SIM card because the card in the old iPad was not compatible with the new iPad Air.

The Apple Store employee was accessing my cellular data account on his iPad.  He asked me for a password.  I gave it to him.  He said no, that won't work to get into your account, I need your SIM PIN.  I told him I didn't know what the PIN was.  He was able to access the account another way.

I have never had to use a SIM PIN to access my cellular data account.

Why would he need the PIN to get into my cellular data account?  The old device never asked for it when I accessed my account in Settings>Cellular.

I'm just worried that somewhere down the line, I'll be asked for this PIN again.

Does that help?

Thank you now it makes sense oh, and he's asking for the wrong thing. What they want is the passcode or security pin for your account. If you don't know what it is you can reset it by logging into your account and ask him to reset the passcode. I'll see if I can find you more information on that for data connect plans. Otherwise call AT&T and ask them how you reset the security pin for your data connect plan. The default used to be the last four of your Social Security number, but AT&T ask people to stop using their social security because it was too easy to guess.

Either 

https://www.att.com/support/smallbusiness/article/smb-wireless/KM1166085/

https://www.att.com/support/article/wireless/KM1001894/

Most accounts currently have an alphanumeric password, and they have a 4 to 8 digit passcode.

AT&T makes it purposely confusing by using similar words to describe two very different things. They should have called the numeric security code just that, or PIN code

Thank you!  Calling ATT is impossible right now because Customer Service currently won't even put you on hold for a next available agent.  Your only options are their (useless) automated voice system and their Chat (which doesn't respond when you click to access it).

Here's the thing:  My plan is a session-based one of long standing (I originally bought it in 2011).  I can only access it through att.com/iPadLanding.  The account overview function there is limited to showing the parameters of each successive 30-day renewal, and the device update function only lets me edit IMEI and ICCID numbers.  Nothing there about security PINs.

 If you've never used a 4-Digit pin code to access your account,  it may still be set to be your last four of your Social Security.   Or it's been 10 years and who remember. 

Unless you have a grandfathered plan that is no longer offered that's a better deal than what is currently offered you are sometimes better off canceling the old plan and just signing up for new.

Not trying to sound purposefully obtuse, honest.

I have a PASSWORD that lets me log in.  (screenshot attached of the login screen)

The FORGOT PASSWORD function seems to me to be where I reset the PASSWORD. (second screenshot attached)

The links you sent look to me to describe resetting the PASSWORD.

They don't seem to refer to the NUMERIC PASSCODE.

Am I way off base here?

Well, that's what I did....except I'm waiting for the current 30-day plan to expire in 2 weeks before the new one kicks in.   That doesn't solve the issue of numeric passcode, though.
I guess I'll just drop this for now.  I've never had occasion to use it, and I'll just have to hope the issue never comes up again.  None of my records from the original device and cellular plan purchase in 2011 refer in any way shape or form to numeric passcodes or PIN numbers.  If I weren't already traumatized by this, it'd be tempting to just chuck it all and go to Verizon.........

Your eyes are fine.  

It's not you... 

Like I said AT&T purposely gave the alphanumeric password and the 4 digit passcode stooopidly similar names.  

And of course other networks have different terms for it so when you talk to someone an apple they are going to ask for something and don't necessarily know that AT&T calls it a passcode, T-Mobile calls it a security pin, and Verizon calls it a pin code.     And those are just the ones I know about.   Calling it a Sim pin doesn't sound right, but I have not had a day to connect plan oh, so it's possible that the data connect plan has a different security code name.  ( because why not make it as complicated as possible 🤣) 

The only time you're ever asked for your 4-Digit passcode is when someone is trying to verify that you are authorized to have account access. Which would happen during an upgrade, anytime you call AT&T about your plan or talk to someone in a store about your account your plan or your devices.  

Re, chucking it and going to Verizon:  I forgot to mention that in order to cancel a postpaid plan you'll probably also need the security passcode. 

You might want to recover then sort that out