The distance from Pushkar to Kolkata is 1600 km. The most practical way is to take a train from Ajmer to Kolkata, which is a long but scenic journey. Alternatively, you can fly from Kishangarh to Kolkata with a layover. The journey takes you across the breadth of India.
Total Distance: 1600 km by road, 1400 km air distance.
This is a very long journey; carry sufficient food and water.
October to March for pleasant weather.