I have to make these medal cookies and I’m just wondering what colours to mix to achieve this golden look
Satin Ice actually makes a gold shimmer fondant that would be perfect for what you need. But you can also get the same look by using white fondant tinted a light yellow and then spraying the pieces with Wilton Color Mist in gold or using an edible gold dust mixed with alcohol or lemon extract to give you a paint like consistency that you then paint on the fondant pieces.
Ditto what Freckles0829 said. Unless you already have edible gold dust, using fondant tinted yellow and sprayed with Wilton gold is probably the best way to go.