>> I have a STP , to Mt Titlis from Lucerne can I buy cable car and rotair at Engelberg itself or before we board the cable car
Buy your tickets at the gondola valley station at Engelberg.
>> Do we have an option to select STP to get 50 % reduction ?
Yes, just show your Swiss Travel Pass when buying the ticket.
>> Trubsee- Alpine Lake is at the first stop at the cable car or second ?
The first. This question is also answered here:
>> Just based on experience, Mid July @ Mt Titlis, do we need to full jacket for snow and cold or light sweater should do good ?
The weather could be anything from mild to chilly, depending on the day. Dress in thin layers that can be added/removed according to the temperature.
>> Mt Pilatus Can we buy the ticket to take the cogwheel at the boat itself ( ride from Lucerne to Alpnachaad ) or only at the cogwheel station or ticket station across the street at train station ?
The Pilatus website has details about where you can buy tickets:
>> Follow up to the above, do they give all the way up back to Lucerne including bus ticket ?
Yes, if you specifically ask for a Golden Roundtrip or Silver Roundtrip. The only difference between them is whether you take the boat to Alpnachstad (Golden Roundtrip) or train to Alpnachstad (Silver Roundtrip).
>> Mt Rigi, Even with the STP pass, we need to exchange for ticket for boat or only for the train up to Rigi ?
Only for the cable car between Weggis and Rigi Kaltbad, if you choose that as part of your route.
>> While coming back , do you guys prefer to come back by boat, get on to weggis and spend some time ? is it worth or Come back to Lucerne via Vitznau
All routes are beautiful, and there is no single route that everyone prefers. Everyone will give you a different opinion. I suggest you read about it for yourself, look at the pictures, and make your own decision.
The only thing I would mention is that if you go up in the cable car from Weggis, the train may be full when you board at Rigi Kaltbad. If so, you will have to stand for the last bit of the journey.
>> My question is on this day we have planned only Mt Rigi , for round trip is it going to take full day or we can spend some time in weggis ( I know some one mentioned for him it took almost 5 to get back to Lucerne but lot of others mentioned whole trip with sight seeting ta Rigi not more than 3-4 hrs. hence my question
What you have discovered is that different people take a different amount of time. It will be up to you how long you spend there, and what routes you take going up and coming down. Use the Swiss Timetable to find out about travel times, then decide for yourself how long you want to spend on top, and what you want to do there. Use the links above and below to assist your planning.