i want to see what is in the backup

Backups are not readable.

Emails are never backed up (basically anything that resides on a server never is, only the account information is backed up).

Messages are backed up only if you have iCloud Messaging disabled, then any message on your device is part of your backup. If you have iCloud Messaging turned ON, then messages are not part of your backup.

Gotcha, yeah no way to slim down a backup other than committing some things to iCloud (which takes them out of your backup). For example, by changing to iCloud Photo Library rather than using Camera Roll, your photos then reside in iCloud and your device, but are no longer part of your backup. That reduces the size of your backup, but of course means that iCloud is the only keeper of your photos (but, pretty dang reliable if you ask me). Same goes for Messages, if you enable that setting in iCloud then Messages is taken out of your backup routine, thus reducing backup size.

Bigger iCloud space might be a better way to solve this for some folks though, or back up locally to your computer (but that can be a constraint too).

How do I get it?

Get what?