From the Super Mario Wiki
Jenny's father first appears at the beginning of the episode, where he stopped to fuel up at the same gas station Donkey Kong Jr. and Bones were at. After he was kidnapped by the Trucknappers, Donkey Kong Jr. and Bones hopped a fence to infiltrate their hideout.
During the climactic fight with the Trucknappers, Jenny's father and the other kidnapped truck drivers were on the verge of falling to their deaths, but Donkey Kong Jr. managed to lasso the truck they were being held in and pulled it back into place, ensuring their survival.
He is not seen again until the very end of the episode, where he thanked the duo for rescuing him, and also for landing the Trucknappers in jail.