In the book "The Call Of The Wild", how does Buck let his masters know that he is the new leader? (don't listen to the questionable)

I'm sorry, what do you mean by "don't listen to the questionable"?

Buck attacked the other dogs..... challenged their leadership, and he didn't let up. He refused to take a place other than lead, and he allowed them to chase him and threaten him with clubs. In the end, they'd wasted so much time attempting to bring him to heel that they had to give him the lead spot simply to get on their way.

Francois sat down and scratched his head. Perrault looked at his watch and swore. Time was flying, and they should have been on the trail an hour gone. Francois scratched his head again. He shook it and grinned sheepishly at the courier, who shrugged his shoulders in sign that they were beaten. Then Francois went up to where Sol-leks stood and called to Buck. Buck laughed, as dogs laugh, yet kept his distance. Francois unfastened Sol-leks's traces and put him back in his old place. The team stood harnessed to the sled in an unbroken line, ready for the trail. There was no place for Buck save at the front. Once more Francois called, and once more Buck laughed and kept away.

“T'row down de club,” Perrault commanded.

Francois complied, whereupon Buck trotted in, laughing triumphantly, and swung around into position at the head of the team. His traces were fastened, the sled broken out, and with both men running they dashed out on to the river trail.