The most succinct Jain mantra is: Namo Arihantanam.

Meaning (arth): I bow to the Arihants, those who have conquered inner enemies and attained kevala jnana (omniscience).

Notes:

• This is the first and core line of the Navkar Mantra. The full Navkar consists of five lines and honors Arihants, Siddhas, Acharyas, Upadhyaya, and the Saadhus, but the single-line form above is the briefest universal mantra.
• There are traditions (Digambar vs. Shwetambar) that present the full Navkar in slightly different order or wording, but the essential idea—bowing to the enlightened beings—is the same.

If you’d like, I can present the complete Navkar Mantra in the respective tradition formats.