Here are some Jain boy names starting with the letter D, with simple meanings:

1. Dhruv – स्थिर, अटल; one who is firm and steady
2. Darshan – दर्शन; spiritual vision, seeing the truth / seeing the Jina
3. Devansh – देव + अंश; part of the divine
4. Dharam / Dharm – धर्म; righteousness, religion, spiritual duty
5. Dharmesh – धर्म + ईश; lord of dharma, one devoted to religion
6. Divesh / Devesh – देवों के ईश; lord of gods
7. Dikshant – दीक्षा का अंत; completion of (spiritual) initiation
8. Dishaank / Dishank – दिशाओं का राजा; lord of directions, one with clear direction in life
9. Dhir / Dheer – धीर; patient, calm, courageous
10. Divit / Divit – दिव्य; divine, bright, sacred
11. Devraj – देवों का राजा; king among the virtuous
12. Dharmik – धार्मिक; religious, pious
13. Darpit / Darpit – अर्पित; one who is offered/surrendered (to religion / right path)
14. Devraj / Devraj – देव + राज; ruler among noble ones
15. Dhaval – धवल; pure white, symbol of purity and non-violence

For a more traditionally Jain flavour, Dhruv, Dharam, Dharmesh, Dharmik, Dhaval and Darshan are especially popular and suitable.