JSON : Fetching a field value from a doctype

I was using webhooks.
How to fetch the mobile number of leave approver in leave application as in JSON format.

Leave approver ->user->Employee ( connected with user ) ->Mobile Number.

"Employee Name":"{{doc.employee_name}}",
"Leave Application":"{{doc.name}}",
"From Date":"{{doc.from_date}}",
"End Date":"{{doc.to_date}}",
"Mob":" ??? "


Can anyone help on this !

Parsing could be the Jinja2 engine. The syntax looks like it.
There is no mention in the documentation concerning variables in Webhook.

Referring to this

In Jinja2 it would be something like this

“{% set la = frappe.get_doc(“User”,doc.leave_approver) %} {{ la.cell_number }}”

is there a way to retrieve doctype info from erpnext from a local computer, fetching datas from doctypes, but notepad or visual code local in another computer? the embbed area of print format with jinja is not well converted to pdf, so I prefer do it with CSS and html. The CSS in jinja print format doesn’t always work.

And is the exact syntax for getting values from erpnext next doctypes, I assume there is a required connection login in the headers or something like that. What is the syntax?