The user creating the work acknowledgement will get a confirmation screen when it is submitted. If they did not get the confirmation screen - the work acknowledgement was not received.
Understand that the work acknowledgment is part of Tablet Mode, which is a web page. When a work acknowledgement is signed and then saved, the information from the web page is immediately sent to ServiceTrade servers. There (and not on your device) it is converted to a PDF, attached to the job, and emailed to the customer.
It is possible that the tech tapped the checkbox "send me a copy" which would send it to their own email as well. We encourage this as a default behavior for this very reason, as it is possible the tech will need to easily retrieve one later, or if it is accidentally deleted from a job.
In most cases where there is no work acknowledgement, yet the tech seems to recall having completed one, there is either weak signal to blame (never got transmitted), or the tech did not save it all the way through (they will see a confirmation screen once this happens).
You can also have the tech revisit that appointment on Tablet Mode. If given the option to "Create Work Acknowledgement" - the work acknowledgment may have not ever been sent. If given the option to "Review Work Acknowledgement" the tech can tap this button and resend from here.