Krypto the dog would beat Thragg.
Every single version of Krypto the dog (Superman's dog) would beat Grand Regent Thragg.
Krypto is as strong to a Dog, as Superman is to a human. Since Superman is around 80~ish sextillion times stronger then a normal human, that means Krypto is 80 sextillion times stronger than a normal dog.
Let's use the doG that's in the newest movie. Since it's based off of James Gunn's dog, Ozu, I'm using his bite force bc what else is a dog gonna do? He's a rescue, terrier mix so let's say around 200 to 250 PSI (pounds per square inch). times that by 80 sextillion and you get 16 to 20 septillion PSI.
So Thragg is getting his limbs bit off. It's not like he'll know either, also he won't know about the Sun so he'll just throw the dog that gets powered up by the Sun closer to it.