Answer

Jambu Kumar Jain pustak generally refers to the Jain life story of Jambu Kumar, who is remembered in Jain tradition as the last Kevali of this avasarpini kaal.

Explanation

Jambu Kumar was a spiritually advanced soul. According to Jain tradition:

• He lived after Bhagwan Mahavir Swami.
• He renounced worldly life and accepted Jain diksha.
• He attained Keval Gyan, complete and perfect knowledge.
• He is traditionally known as the last person in the present time-cycle to attain Keval Gyan.

Books on Jambu Kumar usually describe:

• His birth and family background
• His vairagya, or detachment from worldly pleasures
• His diksha
• His spiritual progress
• His attainment of Keval Gyan

Spiritual Understanding

The life of Jambu Kumar teaches:

• Worldly pleasures are temporary.
• True happiness comes from self-realization.
• Renunciation, right faith, right knowledge, and right conduct lead the soul toward liberation.

Takeaway

If you are looking for a Jambu Kumar Jain book, it would usually be a Jain charitra granth describing the inspiring life of Jambu Kumar and his path of vairagya, diksha, and Keval Gyan.