How can I retrieve a missing "Recently Deleted" album?

Some remarks on deleting photos if you are using iCloud:

• Are you using iCloud Photos and are running out of iCloud Storage? Then you have to be very careful when deleting photos. As long as your iCloud Storage is full, the deleted photos will not be saved in recently Deleted but instantly deleted permanently to help you free your storage immediately. In that case you need to free your cloud storage asap, to ensure that iCloud will again be working as expected.
• If you are using the Shared iCloud Photos Library (just in case the system version  iOS 12 shown below your post is no longer valid) the recently Deleted album will not be showing you photos you are deleting from the Shared Library shared by others - only the photos you shared for yourself.

Just to be sure - you have looked for Recently Deleted in the "Utilities" section in the Albums tab? You have to Tap Albums, then tap Recently Deleted under Utilities (scroll down to Utilities right away and do not tap "Show all" in Albums or you will be seeing less.

The Recently Deleted view holds on to pictures for 30 days (or until you delete from there) before erasing them completely. Then they are no longer retrievable. If you don't see a Recently Deleted folder, then there are no pictures that can be recovered.