login to elite from the web / pc
mouse over browse at the top - click on clan hq
on the top right of the page is a button for "GO TO CLAN SHOWCASE" - click that
then on this screen on the left are two buttons that you can click on to switch between challenges and operations
easy and intuitive huh? lol
you can also sign into elite and go here
https://elite.callofduty.com/competeclick show more at the bottom and you'll eventually see challenges