How to find Apple I.D.# via Terminal Mode

This may read your booted AppleID:

defaults read MobileMeAccounts Accounts | grep AccountID

and for the filesystem on the unbooted Mac:

plutil -p /Volumes/Macintosh\ HD/Users/username/Library/Preferences/MobileMeAccounts.plist | grep AccountID

I'm assuming you put the old laptop into Target Disk Mode to access the data on the old laptop? If so, then the AppleID has no use here since the AppleID is only used by the actively booted OS.

If you are trying to figure out which AppleID this old laptop used, then I'm not sure if it is even possible. Running any utilities to retrieve this from an active OS won't work for an OS that is not booted. Maybe there will be some macOS configuration file somewhere which may have some information on the old laptop, but that information may well be coded for security reasons.

What is your goal here? You should be able to access any locally stored data on the old laptop through Target Disk Mode. If you had data stored in the cloud, then you just need to log into the AppleID used on that old laptop to allow any items to sync with the other Mac (may want to do so with another macOS user account if the AppleIDs are different for the host Mac and the broken Mac.

Or retrieve any documents from a backup made before the old laptop broke.

BillinColoSprings wrote:

Can anyone tell me indetail how I find the Apple ID -- the machine ID, not my personal Icloud id -- in the crashed AMc's hard drive? Thanks in advance ...!

An Apple ID is your personal iCloud ID. It's not a machine ID. If this is your Mac, then it should be using your Apple ID. Or are you saying you had more than one Apple ID?