In the main series of animation Zhen Diamond chapter, Xiao Zhi and his party came to Shuimai City and heard that the owner of the Dojo Hall Donggua went to the nearby Steel Island for special training (but in fact, it was to dig up fossils), so after waiting for Donggua in Shuimai City for a while, Xiao Zhi did not personally go to Steel Island to find him, which is actually a bit inconsistent with Xiao Zhi's personality, and just after Xiao Guang's long-haired pig evolved into an ivory pig, Xiao Zhi and his party heard in the mouth of Miss Joy of the Pokémon Center that the owner of the Dojo In Shui Vein City had returned, so Xiao Zhi naturally planned to go to the challenge immediately. The owner of the museum to be challenged this time, Dong Gua, has a certain relationship with the rock master Whotai that Xiao Zhi challenged before.
PS: This article is purely personal opinion, if there are any errors, please correct.
Related Episodes: Diamond & Pearl Episode 106 "Battle Mallet Dragon VS Moat Dragon"
The owner of the museum, Dong Gua, and his son Lady:

In this episode, Xiao Zhi, who came to the Dojo to challenge, listened to the disciples of the Dojo and said that although the owner of the dojo had returned, it seemed that it was not a good time to challenge, the son of the original Dojo master Dong gua came to the Dojo, and launched a dispute with the Dogua, and Xiao Zhi and his party who entered the Dojo found that The son of the Dong Gua was the dojo master of the Black Gold City that Xiao Zhi had challenged before, and the Dong Gua and the Scoop Tai were both fanatics of fossils, and the topic of their debate was who loved fossils more than who loved fossils. To this end, Donggua showed the fossils of the huge Taikoo feather insect he excavated, and as long as it is restored, this large Taikoo feather insect will definitely cause a sensation.
Togata vs Scoop: Defensive Dragon VS Battle Hammer Dragon
Seeing that the father and son were arguing, Xiao Gang proposed that it was better to use the battle to decide the victory or defeat, so the father and son duo began to fight in this way, Donggua sent a defensive dragon with double resistance as the strength, and the lady sent out the battle hammer dragon with a high material attack base, which can be said to be a spear and shield battle, facing the hammer used by the battle hammer dragon, the moat dragon side used the iron wall to defend, after constantly using the iron wall to increase its durability, the moat dragon began to use moves such as cannon light cannon, flame spray and sticker and battle hammer dragon hard gang, The Battle Hammer Dragon also used the most powerful double-edged head hammer, which was indistinguishable from each other.
Interrupted Battles:
At this time, the Rocket Trio infiltrated the Dojo and stole the fossils that Donggua had collected in the Dojo, the battle between Donggua and Shota was forcibly interrupted, and the final result was naturally that Xiao Zhi and his party chased up and flew the Rocket Trio, but this time it was Dong Gua and Scoop Tai who had been fighting with the Rocket Trio, Xiao Zhi's Pikachu was only the last to close, and then Dou Tai saw that a box treasured by Dong Gua contained a gift he gave to Dong Gua when he was a child. DongGua said that the reason why he came to Shuimai City to become the owner of the museum was to entrust the Kurogane City Dojo to Lady, so the father and son stopped arguing.
At this point, Xiao Zhi can finally have a dojo match with Dong Gua, as for the process and result of the dojo match, let's talk about the next article.