How to attack a two time pad if the plain text is randomized?
If your PRNG is good and your seed unknown $C_R = pt \oplus PRNG(seed)$ is essentially already an encryption of the plaintext using a stream cipher constructed from a PRNG.

Specifically it is indistinguishable from random.

Therefore $K_2 \oplus C_R$ can be viewed as an encryption of $K_2$. This is not useful but it also doesn't help an attacker.

I would conclude that this scheme is just as secure as constructing a stream cipher from a PRNG.