How do I add a field to a child table and get the value specified in the child table

Hello:

I have customized fields in the child table. How can I get the data in other fields?

@Wayne

Considering you want to set values in Purchase Receipt Item Field

frappe.ui.form.on("Purchase Receipt Item", {
    your_child_table_field_name: function (frm, cdt, cdn) {
       let row = locals[cdt][cdn];
       frappe.model.set_value(cdt, cdn, "your_child_table_field_name_where_you_want_to_set_value", row.your_child_table_field_name);
 }
});