What temperature is coffee when you add milk to it?

It is often recommended that instant coffee be made with hot but 'not boiling' water.

If you add hot water first, the coffee will be less than 100 C. If the milk is colder than the coffee liquid, the drink will get cooler slightly, when you add the milk, depending on how much cold milk you put in. If the milk is hot, you will probably not notice any change in temperature, if there is indeed any change.

On the other hand, if you make coffee by first adding milk to the dry instant coffee granules, the coffee will be at room temperature just before you add the milk, and it will rise or fall towards the milk's temperature when the milk as added. Even filter coffee, i.e. made with coffee grounds, will be a little less than 100 c by the time you add the milk.