What is the prefix (उपसर्ग) used in the word 'प्रत्युत्पन्नमति'?

The word 'प्रत्युत्पन्नमति' is formed by the combination of the prefix 'प्रति' and the word 'उत्पन्नमति' via Yan Sandhi ($\text{प्रति}+\text{उत्पन्नमति}=\text{प्रत्युत्पन्नमति}$). Thus, the actual prefix is 'प्रति'.