You'd just connect the DD55's (old-school DIN) MIDI output to either a DIN MIDI input piggybacking on your audio interface, or to a DIN MIDI input on a dedicated MIDI->USB interface. Set a MIDI/Instrument track in Cubase to receive from that MIDI source (input), and you should be able to play & record in Cubase from the DD55. (AFAICT the DD55 is an older (discontinued) device, and doesn't have a direct USB connection, but there are several versions of it, in case yours is really a DD55-something)..
Now, if the DD55 uses standard General MIID note assignments, you should be able to play any standard VI drumkit without further ado; if not, there may be some additional setup required. If you want to record MIDI performances on the DD55 in Cubase and play back the DD55's own sounds, you may need to turn Local Off on the DD55 (see the manual link below, p.26).
Here's the link to the DD55 manual—starting on page 21 it explains using the DD55 with a computer/DAW (the technology references seem pretty old, but it should give you the basic idea). Of course you realize that Cubase 5 is also very old (Cubase is up to version 10 currently), but they should still work together as long as you have the appropriate MIDI connections.
https://usa.yamaha.com/files/download/other_assets/2/319472/dd55.pdf
FWIW, if you need it, here's a link to the Cubase 5 documentation as well (should cover the MIDI connections within Cubase)..
https://www.steinberg.net/en/support/unsupported_products/downloads_cubase_5.html
Note - I've moved this thread to the Cubase forum..
