If you mean Deepak dravya in Jain Ashtaprakari Puja, it is the lamp offering. It symbolizes light, pure consciousness, and the awakening of right faith, right knowledge, and right conduct.

A simple respectful practice is:

• offer the दीपक with bhav
• recite Navkar Mantra
• remember the qualities of the Tirthankar

There is no single compulsory “Deepak mantra” in Jainism. Many Jain devotees simply say:

Namo Arihantanam or the full Navkar Mantra

If you mean a specific Deepak Puja vidhi or stavan, I can explain that too.