He didn't send angels to find out what was going on. He went to Abraham in Sodom and Gomorrah Himself:
Genesis 18:20-21
20 Then the Lord said, “The outcry against Sodom and Gomorrah is so great and their sin so grievous 21 that I will go down and see if what they have done is as bad as the outcry that has reached me. If not, I will know.”
If God is omnipresent, why did he have to send angels to sodom and Gomorrah? Souldn't he know whats going on there without help?
He didn't send angels to find out what was going on. He went to Abraham in Sodom and Gomorrah Himself:
Genesis 18:20-21
20 Then the Lord said, “The outcry against Sodom and Gomorrah is so great and their sin so grievous 21 that I will go down and see if what they have done is as bad as the outcry that has reached me. If not, I will know.”