Hi Corrie! Welcome to RP!
I answered a similar question on another thread.
Perhaps give that a read, then ask me any questions!
However, death knights don’t have jobs. They don’t need to eat or drink or sleep. I’m not familiar with the new lore, but used to be they were required to belong to the Ebon Blade. The Ebon Blade allied itself with the Alliance/Horde, and all other death knights were considered enemies of those factions. So, they are effectively soldiers for the Ebon Blade, which provides them with training, armor, and weapons.
However, the Ebon Blade is usually pretty lax with what it’s individual members do. So, if your death knight wanted to take up side jobs for gold, for whatever reason, they could. My death knight is basically an “adventurer” who occasionally reports into the Ebon Blade.
The way to play a “dark” character without playing an “edgy” character is to know when to, as a writer/player, not take your character too seriously. Give him/her a few funny/good traits. My death knight has no emotions, so I play him deadpan all the time. He works best with a goofier character to highlight his seriousness. But, even without, he occasionally just forgets where he is/what he’s doing (due to death via axe-to-head) and wanders aimlessly, even stopping mid-sentence. Use their being dead as low-key slapstick. Nothing super “comical”, but just a little wink/nod.
The best way to describe it is this quote from WCIII Blood Mage:
The character takes himself incredibly serious, but it’s so over the top, that it’s clear the writer was having fun with a serious character by not taking that character too seriously. It’s pretty meta, and kinda hard to describe.