It is understandable if you cannot remember all the mantras in Jainism. Remembering and reciting mantras is a matter of practice and devotion. The most important and universal mantra in Jainism is the Navkar Mantra (Namokar Mantra), which is considered the essence of all prayers:

णमो अरिहंताणं णमो सिद्धाणं णमो आयरियाणं णमो उवज्जायाणं णमो लोए सव्वसाहूणं

By sincerely chanting this mantra, you pay respect to all great souls and accumulate spiritual merit.

If you wish to remember more mantras, consider the following suggestions:

1. Focus on the Navkar Mantra: It is the most significant and can be recited daily.
2. Practice regularly: Repetition helps in memorization.
3. Write the mantras down: Writing while reciting can aid memory.
4. Learn their meanings: Understanding the meanings helps in deeper retention.
5. Start with short mantras: Begin with shorter prayers and gradually add more as you become comfortable.

Remember, Jainism values sincerity and intention over rote memorization. Even if you recite just one mantra with devotion and understanding, it is spiritually beneficial.