You cannot truly dissolve cinnamon in coffee, even in ground cinnamon form, because it is made of very small wood fibers. If you add ground cinnamon to your coffee, you’ll notice bits of it floating at the top.  The best way to get the cinnamon flavor in your coffee without those bits is by adding it to your coffee grounds before you brew your cup or pot. You can add both cinnamon sticks or cinnamon powder to coffee.