Answer

In Jain Dharma, it depends on the Jain tradition:

• Digambar Jain monks do not wear clothes, including underwear. This is part of their practice of complete non-possession and renunciation.
• Śvetāmbara Jain monks wear simple white clothes, so they may wear basic cloth garments as part of their monastic clothing.

Explanation

The difference comes from the way the two major Jain traditions understand the ideal practice of monkhood:

• Digambar tradition emphasizes total external renunciation, where a fully initiated monk gives up all clothing and possessions.
• Śvetāmbara tradition allows monks to wear plain white clothing while still practicing detachment, celibacy, non-violence, and non-possession.

Takeaway

So, some Jain monks wear simple cloth garments, while Digambar Jain monks do not wear underwear or any clothing.