How to fetch the value of doc.filed_name's from another doctype

else if (frm.doc.purpose === ‘Receipt’) {
// Get the employee field value from the selected asset request
const assetRequestEmployee = frappe.model.get_value(doc.asset_request, ‘employee’);
// Filter assets by custodian matching the asset request’s employee
filters.custodian = assetRequestEmployee;
filters.asset_status = ‘Allocated’;

In the field Asset “Custodian” is showing as empty.

How can I retrieve the value of the “employee” field from the “doc.asset_request” field?

Is there anyone who can assist me?