The World Trade Center site is one of the closest major landmarks to 17 John Street. It's about a 10-minute walk, roughly half a mile northwest, up toward Church and Vesey Streets. Most people come for the two things that sit on the same few blocks: the outdoor 9/11 Memorial, and the tower above it.
Here's the practical version. The Memorial plaza itself, with the two square reflecting pools set into the footprints of the original towers, is free and open to walk through. The 9/11 Memorial & Museum, which goes underground into the story of that day, is a separate paid ticket. So is the One World Observatory near the top of One World Trade Center, where you take a fast elevator up for the view over the harbor and the rest of Manhattan. Both the museum and the observatory use timed-entry tickets, so if you're visiting in a busy stretch it's worth booking a slot before you leave the suite.
We get a lot of guests who want to do this in a half day. It works well from here. Walk over in the morning, spend time on the plaza, pick one of the paid sites, then loop back toward the water or over to Stone Street for lunch. Below is how we'd lay it out, plus what's worth knowing before you go.