First you would need to determine which military facility he is operating at - if at all possible (some deployments are sensitive in nature and all that families can be told is what country a soldier is operating in). That will narrow down where you would need to search in the database to see if any current channel/talkgroup information exists to load into your scanner - assuming, of course, a) you are close enough to the facility to monitor it directly, and b) you have the right kind of scanner to monitor the facility (many are using APCO P25 systems). If not, the next step would be to determine if any on-line feeds exist for that facility that you could tap into.