My son and I will be arriving June 1-12 & want to buy the 15 day Swiss Rail Pass. When do you recommend we buy them? How far in advance? Do we also need to make reservations on the trains? Our home bases are Lucerne, Wengen, Zermatt and Zurich. Thanks!
You can buy them when you arrive in Switzerland, assuming you are arriving by airplane. The only trains that require reservations are the Glacier Express, Bernina Express, Gotthard Panorama Express. From the bases you mention, you probably will not be doing any of these. Just board the train and show your pass when the conductor comes by. Have your ID handy in case the conductor wants to see that as well.
I like to purchase a few days before I leave the US. That way I can print out a few copies at home. I find it easier to show a paper copy of the Pass as I can just keep it out on the train table until the conductor comes around. And it’s nice to have a paper copy as a backup in case something happens to your phone.