When making a record, in the "Trace Number" column a trace number can be entered, it would be every useful to have a number automatically generated, it would save time and be very convenient for the one who does the imputing.
While a good and useful suggestion, the commenter below has inadvertently demonstrated the significant technical hurdles to achieve what you ask, on the face of it. However what you have not mentioned is where you would require this functionality, so lets explore that before jumping to conclusions that product change is required. Lets assume for a moment that you are using the Batching Module to generate Product Batches and it is here you need to automatically generate traceability numbers.
What is a traceability number? It is an identifier for a specific batch of product. The format it takes is entirely irrelevant as long as it uniquely identifies a batch of product, therefore why not use the automatically generated Record number for the batch? And if you wanted you could combine that with the current date in Gregorian date format as many food companies already do for their traceability codes. So if the date is the 31st of October 2015 and the batch record happens to be 236 then the Traceability number is 20151031236.
On the other hand if you are referring to the Trace no. column in the Monitoring Record then this column is not mandatory so you can leave it empty.