How do I determine total fare cost to travel from Lauterbrunnen -->Wengen-->Kleine Scheidegg-->Grindelwald by train?
I will be having a Swiss travel pass.
I check the SBB.ch website,but somehow it does not show fare cost with Swiss travel pass.
Use this map to figure the discounts:
https://www.swisspasses.com/railpass/overviewmap_en.pdf
From Lauterbrunnen to Wengen your cost is covered with a Swiss Pass---so no cost. From Wengen up to Kleine Scheidegg and down to Grindelwald, you are on the portion of the Jungfrau Bahn with only a 25% discount given to holders of the Swiss Pass.
So use SBB.ch to find the cost from Wengen to Grindelwald via Kleine Scheidegg ( I believe it is 53 CHF but check that) and take off 25%. That will be your cost.
You can also see fares for that region in chart format at http://www.jungfrau.ch/en/tourism/travel-information/tickets-rates/lauterbrunnen/fares-for-individual-travellers/ and see the little map for discount ranges with different passes.
If you want to use the charts, it would be easier to use Wengen as the starting point, since Lauterbrunnen to Wengen is free.
This chart also includes Wengen to Grindelwald via Kleine Scheidegg ( 53 CHF) so the only calculation necessary is the 25% reduction.