The following code effectively displays the dog's names and when selecting a dog, it outputs its color. What I would like to do is be able to track what object has been selected and be able to access all its attributes in the onChange method.

How can I access all attributes of the selected object inside the onChange method?

    class Dog:NSObject {
        var name = ""
        var color = ""
        var breed = ""

        init(name: String, color: String, breed: String) {
            self.name = name
            self.color = color
            self.breed = breed
        }
    }

    class DogService:ObservableObject{
        @Published var dogs:[Dog]

        init(){
            dogs = [Dog(name:"Pluto", color: "Brown", breed: "Golden Retriever"),
                    Dog(name: "Teddy", color: "White", breed: "Poodle"),
                    Dog(name: "Rocky", color: "Black", breed: "Labrador")]
        }
    }

    struct PickerTest: View {
        let dogService = DogService()
        @State private var selectedDog = ""

        var body: some View {
            Form {
                Picker("Dogs:", selection: $selectedDog) {
                    ForEach(dogService.dogs, id: \.self) {
                        Text($0.name).tag($0.color)
                    }
                }
                .onChange(of: selectedDog) {dog in
                    print("Dog Color: \(dog)") // outputs, Brown, White or Black

                    // what I would like to do...  
                    // print("Dog Breed: \(dog.breed)") // should output, Golden Retriever, Poodle or Labrador
                }
            }
        }
    }

Hi. Just change your tag to refer to breed instead of color, like so

 var body: some View {
        Form {
            Picker("Dogs:", selection: $selectedDog) {
                ForEach(dogService.dogs, id: \.self) {
                    Text($0.name).tag($0.breed)
                }
            }
            .onChange(of: selectedDog) {dog in
                print("Dog Breed: \(dog)") // outputs, Brown, White or Black

                // what I would like to do...
                // print("Dog Breed: \(dog.breed)") // should output, Golden Retriever, Poodle or Labrador
            }
        }
    }

to access all properties then assign dog object to a tag.

@State private var selectedDog = Dog(name: "", color: "", breed: "")

    var body: some View {
        Form {
            Picker("Dogs:", selection: $selectedDog) {
                ForEach(dogService.dogs, id: \.self) {
                    Text($0.name).tag($0)
                }
            }
            .onChange(of: selectedDog) {dog in
                print("Dog Breed: \(dog.breed)") // outputs, Brown, White or Black
                print("Dog Color: \(dog.color)")

                // what I would like to do...
                // print("Dog Breed: \(dog.breed)") // should output, Golden Retriever, Poodle or Labrador
            }
        }
    }