If you're looking for a meeting place or a good stop around ½ or halfway between Dumka and Jahanabad, India, you can try Jamui, India, which is about 3½ hours northwest of Dumka, or about 4 hours east of Jahanabad, India.
About ¼ or a fourth of the way, you can stop at Jasidih, India. This is about 2 hours northwest of Dumka.
About ¾ or three fourths of the way, you can stop at Rajgir, India. This is about 6 hours northwest of Dumka, or about 2 hours southeast of Jahanabad, India.
If you drive straight through without stopping at all, the total distance is 313 km. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 7 hours, 44 minutes.