Janamejaya Guru's

When Janamejaya became eleven years old, 

1. the family priest initiated him duly with the Gâyatrî mantra and he also studied it duly. 
2. Then Kripâ chârya taught him perfectly the science of archery (Dhanurveda) as Dronâchârya taught Arjuna and Paras'urâma taught Karna. 
3. Janamejaya learnt by and by all the sciences and became very powerful and indomitable to his enemies as he was skilled in the science of archery, he was similarly in the other branches of the Vedas. Truthful, self-controlled, religious, the king Janamejaya acquired full knowledge in the Dhârmas'âstras (philosophies and law books) and Arthas'âstras (economics) and governed his kingdom like the Dharma's son Yudhisthira.

https://www.sacred-texts.com/hin/db/bk02ch11.htm