The name itself might give you a clue, or just look at the code: https://github.com/tevador/RandomX

Yes, but how can JIT be a requirement, people sufficiently determined could keep the JIT output and then there's no need for it any more.

Each hash input generates a code sequence that has to be executed 1000s of times in an inner loop. The code sequence is different for each input meaning there is no reason to save the JITted code as the next hash will use a new code sequence which you cannot predict.

  data = input;
  for (1..10)
  {
     JITtedCode = CodeGen(CryptographicHash(data));
     for (1..100000)
     {
        data = JITtedCode(data);
     }
     data = CryptographicHash(data);
   }
   output = data;