which metro to take from capitol south to the cathedral?

Take Capitol South to Metro Center, transfer to Redline - take to Dupont Circle - use Q ST exit, walk south to 20th & Mass Ave NW, board N6 bus, get off Wisconsin Ave., cathedral to your right.

There is good street parking that is free if you drive especially open on a Sunday

There is no close subway station, but buses are nearby.

It's a 22 minute walk from the Cleveland Park red line stop.