Jacen was there as Best Man, he's still not entirely there with being social but you wouldn't have known it looking at him. He was friendly, involved trying to talk to everyone he could.
He was dressed simply, not in Jedi Robes but in clothes fitting for an occasion such as this.
His speech was a good length without being long. There were embarrassing childhood stories yes, but mostly about how Tahiri had been a part of their family since forever but now it was official and he and Jaina welcomed his new sister. He said Anakin had helped him through the worst parts of his life and never wavered in his belief in him and that he deserved happiness always.