https://www.si.edu/ohr/jobs_public

Some of these are temporary listings, and some require experience within SI to apply. It's still worth a look, though. There are even openings for the Smithsonian-adjacent ventures, like the IMAX theater at Air & Space.

The Holocaust Memorial Museum isn't a Smithsonian museum, and won't be on that list. Neither will National Gallery of Art, or any of the other private/self-operating museums in DC. They'll have respective "jobs" sections on their sites, though. It's definitely worth doing some digging.

Best of luck!