Soul Food at the Grocery Store
What's a grocery store in DC that will carry collard greens, ham hocks, ect. My sister wants to make some stuff, but doesn't know where to go. She also doesn't have a car, so if it's near a metro stop that's even better.
I would go to Eastern Market. The greengrocers there will have collards, and towards the southern end (Near the bakery) you'll find a vendor that sells smoked hocks but also smoked turkey necks and wings. you can also buy hot smokes and lots of other sausages there as well as salt pork, Tasso ham, and generally pork in all its guises
Although not technically a grocery store, I think your sister might also enjoy checking out the Florida Ave Market.