Comment on photos in shared albums in iCloud
You can comment on or like any photo or video in a shared album you own or subscribe to.
In the Photos app on your iPad, tap a shared album.
Tap a photo, then tap “Add a comment.”
Enter a comment, then tap Send.
If you own a shared photo album, you receive a notification when a subscriber adds a comment to or likes a photo or video in your shared album. If you are a subscriber to a shared album, you receive notifications when another subscriber has commented on or liked a photo or video only if you’ve already commented on it or liked it.