When a check copy is uploaded from the purchase order an email notification is sent.

To add the sales order number, first the sales order to be get from the sales order record by using the code:
var tranid = record.getFieldValue('tranid');
Then this variable has to be used in the Email body to get the sales order number in the Email Notification.
if (SOId) {
if (source == "Web (The Artina Group Inc. SCA)") {
//nlapiLogExecution('debug', 'source web');
var emailSubject = "Check Copy has been uploaded";
var emailBody = "<html>The check copy is uploaded successfully with the Sales order number:"+ tranid +"<br><br><br></html>"
var emailSend = nlapiSendEmail(senderEmailToUse, "info@formsfulfillment.com", emailSubject, emailBody,null,null,records);
//nlapiLogExecution('debug', 'emailSend', emailSend);
}
else if (!source) {
//nlapiLogExecution('debug', 'source UI');
var salesRep = record.getFieldValue('source');
//nlapiLogExecution('debug', 'salesRep', salesRep);
var setby = record.getFieldValue('recordcreatedby');
//nlapiLogExecution('debug', 'setby', setby);
var emailSubject = "Check Copy has been uploaded";
var emailBody = "<html>The check copy is uploaded successfully with the Sales order number:"+ tranid +"<br><br><br></html>"
var emailSend = nlapiSendEmail(senderEmailToUse, setby, emailSubject, emailBody,null,null,records);
}

Then the sales order number will be attached in the Email Notification.