Need information in getting swiss pass

Swiss rail is expensive enough such that you might benefit from a Half-Fare Card despite having a Eurorail pass. You can buy them at the first Swiss rail station you visit. They cost about 120CF per adult (kids under 16 ride free with their parents). The HFC grants you a 50% discount on any rail, cable car, or boat tickets.

Thanks. I am trying to understand so that I can be prepared in purchasing tickets and plan my trip as well.

After getting half fare card, should I still purchase any tickets at the station while visiting the places i mentioned in my itinerary within swiss. Please calrify.

After getting half fare card, should I still purchase any tickets at
the station while visiting the places i mentioned in my itinerary
within swiss. Please calrify.

The half-fare card is only a discount card, so you will still need to purchase tickets as you go. If children under 16 years are traveling with you, ask for the family version of the card. This will allow the children to accompany you for no additional charge. The half-fare card is valid for 30 days. More details here.

I count 7 journeys:
1) Paris to Venice
2) Venice to Luzern
3) Luzern to Titlis return (day trip).
4) Luzern to Interlaken.
5) Interlaken to Jungfrau return (day trip).
6) Interlaken to Geneva.
7) Geneva to Geneva airport?

• Paris to Venice: see here for info about trains: https://seat61.com/international-trains/trains-from-Paris.htm#Paris-Italy This is a long way, a train takes all day. I would consider flying, or taking a night train, but then you have to add cost for sleeping accommodation, which is not included in a pass.
• Luzern to Titlis. Titlis is not covered by your pass.
• Interlaken to Jungfrau. This is also not covered by your pass.
• Interlaken to Geneva. and Geneva to Geneva airport?. Is this in two different days? Are you planning to stop overnight in Geneva? If not, it is just one journey. Geneva town to Geneva airport only costs CHF 2. It is not worth wasting a pass day for that trip.

You can look up times and prices for all Swiss trains on the SBB website: https://www.sbb.ch/en/

I would seriously re-consider if a Eurail pass is a good idea. I suggest you calculate the cost of buying tickets Paris - Venice (advance purchase, rail or air), and Venice - Swiss border (Chiasso); and buy a half price card for Switzerland only + ½ price tickets for each trip in Switzerland. The ½ price pass gets you discounts on the mountain railways as well, which a Eurail pass does not.
Look up Italian advance purchase prices on Trenitalia, not on a reseller.

You have to do some arithmetic, but you may save money.

Re: half price tickets. On Swiss ticket machines there are two buttons "full price" and "½ price / child". If you have a half price card, you pay the child fare.
For example, Luzern to Interlaken Ost is CHF 33 full price, or CHF 16.50 ½ price.
Interlaken Ost to Genève is CHF 72 full price, or CHF 36 ½ price.

If you have a Eurail Select Pass for three countries, I would not get a separate Swiss pass or discount card. That pass covers you to Engelberg and gives you a 50% discount on the Titlis cable car. From Interlaken, it gives you 25% off the routes to Lauterbrunnen, Jungfraujoch, and Schilthorn. (We prefer to stay in Lauterbrunnen or further up a mountain, rather than in Interlaken.) See coverage described at https://www.ricksteves.com/travel-tips/transportation/trains/switzerland-rail-passes.

If you are flying from Paris to Venice (see www.skyscanner.com), then I'd get a Swiss Travel Pass or Half Fare Card plus a separate train ticket (advance-purchase discount available) from Venice to the border crossing at Chiasso.