Jun 26, 2015 - 10:24 AM
a) You first need to travel to Interlaken Ost. Please see the Jungfraujoch page for the rest of the route. It's a very long trip from Geneva, more than 5 hours one way. I would normally not recommend this as a day trip. If you don't mind the amount of traveling, then be sure to check the weather forecast before you leave.
b) I am not sure which one day pass you mean. Is it the one discussed here? If you already purchased it you can ask the point of sale about the validity. In either case, you can visit a staffed service desk at the rail station, show the pass, and they will be able to sell you any additional tickets if required.
The Swiss Travel Pass validity can be found here.
c) Please see the Jungfraujoch page for what to expect there.