Like moon-buddy said, you can't really query a specific backup, that's because once on the TSM Server, each object is an individual object, they are not part of a group (unless you did a backup group, but you said selectivce). If you know the start date/time and the end date/time of the backup though, you can use use -fromdate and -todate to cover just the period of that backup.
dsmc query backup {filespec} -fromdate=... -fromtime=... -todate=... -totime=... -su=yes
You can use "dsmc help" for the syntax of these options.