You have to reach to Rishikesh or Haridwar from your destination,which is Jaipur as you said.you can travel by road till Gorikund .After wards you can trek .This is a 14 kilometer trek from Gorikund to Kedarnath
From jaipur you can board a train till haridwar or rishikesh. there are plenty of buses in the morning to sonprayag from haridwar and rishikesh both. if one does not get a bus to sonprayag then catch a bus till rudraprayag from there shared jeep to sonprayag. After reaching sonprayag there are shared maxi cab which charges 20rs. till gaurikund which is the last motorable road. From gaurikund one can trek 16 kms to reach kedarnath. hope this answer helps you in planning your trip.