I just did this solo (thanks to the tips below from other guardians) by jumping through the hole above the door to the bridge, and it was super-easy. I found the knight, popped a 3 of coins and killed him with one clip from my machine gun plus a little but of lightning super in like 12 seconds. And the 3 of coins definitely works, I got an exotic special engram to drop, (and it was my first use of the week)! I like the emblem, too, it's pretty sweet. Thanks to all the people who posted about this!