The correct option is C somniloquist
Option C is the correct answer because a somniloquist is one who talks while he is asleep, which is the most suitable substitute for the given statement, as “somniloquy” is the act of talking In one’s sleep.
Option A is incorrect because “somnambulist “ means one who has the habit of walking in sleep, as somnambulism is sleepwalking .
Option B is incorrect because insomnia means lack of sleep, hence “insomnist “ is one who doesn’t get enough sleep, or is suffering from lack of sleep.
Option D is incorrect because “blabberer” means someone who blabbers, which means to talk foolishly and excessively, hence it is not the same as sleep talking so it is incorrect.