My icon for photo is missing not only from dock but from launch pad on my MacBooks Air
The quick way to find any app you might be able to delete is open the App Store app and find the app using search. 


if the app is deleted, you can reinstall it
if the app is just moved, you can open it


Once it’s open, keep it in the dock with a control click or right click. Spotlight can help you find the app in finder if you need to put it back in the Applications folder