Not sure of what you are asking for.

Tapes have labels written to them. You don't see that with the mt command. If you are wondering what is on the tape, check out the man pages for tar, cpio, dd, and ufsrestore (do this one in interactive mode - then you can see what is on it without restoring). The hard part is finding out which format it was made with (if that is your problem).

If you are only trying to figure out what the tape device is, look at /dev/rmt. It will have a list of devices (some may be old and not work - one of the 'stupid' things in Solaris - put a tape drive on a server, remove it, put it back and it won't see it - you have to recreate it and it gives it a new id - there are ways around this but I've never seen too many folks blow away the old. It just stays there like an old VMS system).