See https://www.ricksteves.com/travel-tips/transportation/trains/reservations and follow the links to the countries where you plan to travel.
Three of the four trains that you mention require reservations, which you can make at the same time that you buy the pass (a good idea for Paris to Geneva, since these places are limited, but note that it's an expensive reservation). Italian seat reservations could be made later in train stations if you're not yet committed to specific departures. The Golden Pass train doesn't strictly require reservations (except for groups), but they're recommended for the panorama car on the Montreux-Zweisimmen leg of the route and http://www.goldenpass.ch/en/goldenpass/offer/index-lines is another place the reservations are sold.
In general, the Deutsche Bahn train schedule link Looking Up Train Schedules and Routes Online is the best resource for knowing which trains require seat or sleeper reservations. But note that for Italian trains, this site no longer uses the obvious phrase "subject to compulsory reservation," but instead the details say "Global price," which actually indicates the same thing.