What episode was it when nicol in gundam seed had a concert and athrun fell asleep?

That scene doesn't occur in Gundam Seed. It seems you might be mixing up details from different anime or have a misconception.

* Nicol Amarfi is a character from Gundam Seed Destiny, not Gundam Seed.

* He doesn't have a concert in either series.

* Athrun Zala is the character who falls asleep in a significant scene, but it's not during a concert. It's during a meeting with the Earth Alliance Council in the Gundam Seed Destiny episode 11, "The Promise". He falls asleep out of exhaustion and stress.

It's possible you're remembering a scene from a different anime or perhaps your memory is playing tricks on you!