If your journey is from ISBT Kashmiri Gate, you can take a direct bus to Kurukshetra, but the journey time becomes quite long by bus.
Otherwise, you can take a bus that goes by the route of Punjab or Jammu, which will decrease your journey time to 3 hours. You will arrive at Pipli, then take an auto and within 20 minutes, you will reach Kurukshetra
You can choose any of these routes based on your convenience