Hi neux,
Welcome to Apple Support Communities.
The article linked below should answer your question about how to view requests and why you may no longer be able to view the notification, specifically if the request is more than 24 hours old it will be deleted.
Request and make purchases with Ask to Buy - Apple Support
Make or decline a purchase
If you're the organizer, you can use these steps to make or decline the purchase from your iOS device with iOS 8 or Mac with OS X Yosemite:
- Open the notification to see the item that your family member wants to get. (See your notifications on your Mac or iOS device.)
- Approve or decline the purchase.
- If you approve, you need to sign in with your Apple ID and password to make the purchase.
After it's purchased, the item is added to the family member’s account and shared with the rest of the family group. If a family member downloads a previous purchase again, downloads a shared purchase, installs an update, or uses a redemption code in the store, the organizer won't get a notification.
If the organizer doesn't make the purchase or decline the request, it will be deleted after 24 hours, and the child will need to make the request again.
Cheers,
-Jason