How to get createdAt time zone form webhook?

This date does not provide time zone information and looks like it uses the account time zone.

Yes.

Is it possible to specify the date format in webhook template?

No.

Is it possible to get an account time zone from webhook?

No, unless you manually pass it as a field.

P.S. Format "yyyy-MM-dd hh:mm:ss" is not the best practice for the program interface.

It's valid ISO 8601 local. I don't know what you mean by "best practice" unless you're referring to the absence of an explicit timezone for transport outside the system.

No, unless you manually pass it as a field.

Duplicate system time zone in the webhook template is not a good solution. Does it possible to request a new system token: {{system.timezone}}?

An alternative solution is to provide a possibility to set date format in the token: {{createdAt:format=yyyy-MM-dd'T'hh:mm:ssZ}}

It's valid ISO 8601 local. I don't know what you mean by "best practice" unless you're referring to the absence of an explicit timezone for transport outside the system.

Yes. Local date is fine for user interface but not for the system to system communication.