He is involved in the following quests:
"I'm out of my element, eh? Walt doesn't know what he's talking about! I single-handedly kicked the iron out of these dwarves and set up camp to observe the goings-on of the dig site."
Donny and his reference to being 'out of his element' is a subtle nod to a character of the same name in the Coen Brother's film, The Big Lebowski, in which his war veteran friend named Walter tells Donny that he's out of his element whenever he attempts to join the conversation between the main characters. A nod to Walter also features in the game - Walt.