You could create a report that uses the User Name dimension and add a filter on the specific userID you are interested in. Then you can add Application, server IP or any other dimension. The report will show only the traffic from that specific user. However this will only work if it is HTTP or any other protocol that you can extract the user name from. You could also do the same thing by using client IP, if you know that the service account is always going to be using the same IP address.