where are the people tags stored in photos

It is part of the photos database - you will never find a single file with useful info in it.

One way to protect the tagging is to select all the photos of one person and add a keyword of that persons name. Then if the name tags are lost you can easily re-add them by searching for that keyword.

2609W wrote:

I keep losing tags when i update the system. Wondering what file is keeping this info

when you upgrade to a new major system version, the algorithm for the face detection may have been improved and then Photos will scan again for faces. The new algorihm may discover additional faces, miss previously detected faces, of find them in a slightly shifted position. In that cat Photos will need our confirmation, foe it can use the previously assigned faces names.

It helps to wait until the new faces scan has been completed, and then to use the command "Confirm additional faces" for each people album. Only if there are still missing faces in a month or so, assign the missing faces again. That is, when the keywords with the previously assigned faces names will come in handy. I am using smart albums with rues like "Keyword is Mickey and person is to Mickey, or similar.

TonyCollinet wrote:

One way to protect the tagging is to select all the photos of one person and add a keyword of that persons name. Then if the name tags are lost you can easily re-add them by searching for that keyword.

Not only that, but keywords can be exported with a picture, but face tags can't. Face tags are only useful inside of Photos. So if you want to send a picture to someone, keywords can help them, but not face tags. As Tony says, face tags are mostly a big help to apply useful keywords.