If using an external USB midi device to connect the TD-9, then it is the midi device to look for in Cubase, not the TD-9.
The midi device should perhaps have USB drivers installed too.
TD-9 mid-out > UM-1 midi-in.
TD-9 midi-in > UM-1 midi-out
The TD-9 will not "appear" on the PC or Cubase.
The um-one should.
If the um-one is working correctly, then connecting the MIDI out of the TD-9 to the MIDI in connection of the um-one is the way to go.
The TD-9 will no doubt be transmitting on MIDI ch. 10, but if Cubase is like any other DAW I've used any MIDI activity will show up, usually with some form of MIDI receive indicator.
Does the um-one have any MIDI data LED's, and are they doing anything?