You need to exspand the instrument in the instrument list (using the drop down menu fro the instrument) to be able to check of availble multi outputs for that instrument. Each check of create a new channel in the mixer.
Also you need to set the instrument that has multi output up. Check your manual etc on how to do that.
There are many infos about Kontakt on the web - including in NI websites knowleadge base. Just search for it. Can take some learning to do it.
Hope this helps.