Use the Amtrak bus system from San Jose Caltrain Station to San Luis Obispo. It s possible to catch the Starlight train from the station, but time and convience wise, won t make much difference. Amtrak bus from San Jose to SLO takes about 4hrs, as it s a straight shot down HWY 101. Check with Amtrakwww.amtrak.com/
You need to take Greyhound, CalTrain is for San Jose to SF only, it doesn t go to SLO:http://www.greyhound.com/Cost is approximately $40 one way and takes 5 hrs.
The ONLY train going from San Jose to San Luis Obispo is the Amtrak Coast Starlight . You can book a reservation at www.amtrak.com . I believe it only runs once a day.