where can i find doc about this?

I was searching for market cap and found this stackoverflow question
On the first answer there is a link to get data of coins in binance.
However when I tried to find the description of the link at binance documentation but I could not.
I would love to see description about this in binance doc
where can I find it?

The shared https://www.binance.com/exchange-api/v2/public/asset-service/product/get-products there is not an published API, therefore not in the API Doc.

With the published API, I don’t think there’s a field where we could see the total number of an asset that has been mined in order to calculate the market cap.

where could have the answerer found info about the unpublished api?

The user most likely reverse-engineered the Binance UI frontend.

This approach is not suggested as these endpoints can and will be changed without prior notice.