Who did Percy fight in the 2nd titan war other than Kronos(he fought that sun titan or something what was his name?)

He fought Hyperion, the titan of light, and Kronos's brother.

In-depth answer:

This took place in the Last Olympian after Annabeth recovers from the kutsilyo she took for Percy. Hyperion, the titan lord of light and ruler of the east (which was the most powerful of the four) during the Golden Age of the Titans, leads an attack towards the Empire State Building. However, he doesn't wait for the army to advance. He charges straight toward Percy while walking on water. While Annabeth and the others keep the monsters busy, Percy fights Hyperion on the water but soon gets pushed out onto land where Hyperion tries to strike him down. Percy, being the son of the god of hurricanes, causes a mini-hurricane at his feet, blowing Hyperion off his feet. He continues to fight him and finally brings him over to Grover and the other satyrs who begin to play a song on their reed pipes causing a puno to imprison Hyperion before he can regain his strength.

Hope this helped!