Nice idea to send him/her good wishes. Here are simple, respectful phrases you can say or write to your friend going to a Jain tirth (pilgrimage). You can mix and match as you like.

Short blessings

• Jai Jinendra! Wishing you a safe and blessed yatra to the tirth.
• May your tirth yatra be peaceful, protective, and spiritually uplifting.
• Safe travels to the tirth. May you have darshan, vrata, and inner calm.

In Hindi (more devotional)

• जय जिनेन्द्र! आपकी तीर्थ यात्रा मंगलमय और शुद्ध भाव से हो।
• सुरक्षित यात्रा हो और तीर्थ दर्शन से आपका मन शांत हो।
• तीर्थ यात्रा सुखद रहे, और सही धारणा/कर्म आपको आचरण में निखार दे।

Encouragement with Jain values

• May you practice ahimsa (non-violence) and SIT (shikshan, inner reflection) during your travels.
• May your vrata and tapas (austerities) deepen, and may you return with a clearer heart.
• Remember to be mindful, gentle, and respectful to all beings during the yatra.

Warm, friendly options

• Have a wonderful yatra! Can’t wait to hear about your darshan and experiences.
• Travel well, friend. May you return with peace, light, and new inspiration.

If you want, tell me a bit about your friend (their name, mood, how formal or casual you want to sound), and I can tailor a few lines exactly for them.