I cannot find a job
Search takes a job number, a surname, a phone number or a serial. If none of them find it, it is probably finished.
Search everything
The search field at the top takes a job number, a surname, a phone number or a serial number. Partial matches work: three digits of a phone number is usually enough.
Check Done and Still here
The board shows open work. A job collected last month is not on it. Search covers everything regardless of status, so if search finds nothing the job is not there under what you typed.
Try the customer
Open the customer record and look at their history. People misremember their own job numbers constantly, and half of these turn out to be a different item from the one being described.
Deleted jobs
Only an owner or manager can delete a job, and a deleted job is recoverable for thirty days from Settings → Data → Recently deleted.