On the lines from Interlaken, there's a 25% discount. You don't need to use a travel day.

Details of coverage in Switzerland are on this map.

If you are planning to spend some time in Switzerland you might want to take a look at the Swiss Travel Pass which includes several of the trains that not are included in Interrail/Eurail.

https://www.sbb.ch/en/leisure-holidays/inspiration/international-guests/swiss-travel-pass.html

If you have specific questions regarding travelling in Switzerland, please feel free to ask. My family and I have just returned from a trip there.

Even with this discount normal fares in this area are superexpensive. There are also LOCAL passes that last just a few days and cover these lines-ANY station-and in fact also near every ho(s)tel etc or tourist info has loads of old-style brochures and info about that. However, this oso famous trip to the Jungfrau is never covered in any pass-discount only and can still cost near half the cost of your total pass for just this return-high up in the mountains with a load of other screaming tourists

What are the local passes that I would need to find?  I have already purchased my eurail pass

If you already have the Eurail pass you shouldn't by any other pass. Then you'll just have to decide if you want to spend the money going to Jungfraujoch.

If you want to do a trip in the Jungfrau-area I personally would skip Jungfraujoch and go to Mürren and Schilthorn where one of the James 007 Bond movies was partly shot instead. The turning restaurant is nice and in an hour you get to see a 360 degree view of the mountains around.

To be sure to get a seat in the restaurant you need to make a reservation in advance. If you travel during high season allow enough time for the travel up to Schilthorn so that you don't miss the reservation in the restaurant.

https://schilthorn.ch/en/welcome

I am looking that Lauterbrunnen to Wengen is part of the SBB system and therefore is part of the Eurail Global pass, is this accurate?

No Lauterbrunnen - Wengen is not part of Eurail (This route is not operated by SBB)